Again, I didn't feel like I needed to make the disclaimer that I realized standard and limited are not cube, but I guess I did. My point is that other formats can and do inform cube testing decisions and provide a limited degree of predictive value of the likelihood of success in other formats. Of course there are standard all-stars or limited bombs that don't translate to cube and I'm not saying that success in other formats determines a card's success in cube. At a time, when I can't get the group together to cube, I'll take early cues where I can get them -- particularly on MDFC's which are still an unknown.
I'm watching the ZNR preview streams like a hawk to see how effective the MDFC's are. I've only watched 3 decks so far W/B Clerics, U/B Rogues, and Mono-Blue Mill. Initial impressions are that it is telling that the streamers who tend to excel at deck construction (CGB in particular) are running playsets of these. I didn't see any of these cast as a spell except for one game where the mono-blue deck was able to cast Sea Gate Restoration right before dying but to be fair mono-blue mill is not a great deck period. Hoping to see some builds running the G/R MDFC's.
Verdict is still out, need to watch some more. Also, yes I know that Day 1 standard with ZNR doesn't necessarily predict performance in cube, but it is better than nothing.
Incidentally, this caused me to go back and look at the top sets for my cube, and I was surprised. I tried to move everything around to their "original" printing, but my method was an imperfect science. Here are all the sets (lumping ABUR together) with 10+ cards. I hadn't realized that MH1 has more presence in the cube than ABUR does.
MH1 (18 inclusions) was a monster of a set largely due to the Canopy land cycle and the talismans. ELD has 13 inclusions for me and none are land cycles.
Fabled Passage
Stonecoil Serpent
Gilded Goose
Once Upon a Time
Bonecrusher Giant
Brazen Borrower
Murderous Rider
Oko, Thief of Crowns
Questing Beast
Rankle, Master of Pranks
Embercleave
Garruk, Cursed Huntsman
The Great Henge
No other set comes close (so far) if you take out land cycles (shocks/fetches). This one will come very close I expect at least 10 to stick.
Here's a thread to compile your likely inclusions and/or cards you want to test from ZNR. As always, feel free to expand your list as spoilers continue to drop or just drop your list at the end of spoiler season.
Likely In Luminarch Aspirant - A free +1/+1 counter wherever you want on each of your turns is huge value. Works great in aggro/tempo and isn't a poor late game draw either. Also a human, which is huge for those running Champion of the Parish. Jace, Mirror Mage - Seems to be about on par with Jace Beleren, but infinitely more interesting. Thieving Skydiver- Great tempo card, but that steal a mox, steal an equipment (not you Skullclamp)ability is what makes this a shoe-in for powered cubes and still a strong option for unpowered. Nighthawk Scavenger- Nearly a strict upgrade to Vampire Nighthawk. Easy swap for those running that and probably better than some of the options people are running over Vampire Nighthawk. Kargan Intimidator- The only other cubed red 2-drop threatening 4 damage on turn 3 is Bloodrage Brawler and discarding a card is a steep price for aggro (less steep if reanimator is part of the gameplan). This threatens 4 damage, can turn off a blocker, can trample over blockers, and may have incidental warrior synergies. Turntimber, Serpentine Wood - The best of the MDFC's by a lot. The mythic cycle allows players the option to negate the loss of tempo when an untapped land is needed by taking a bolt to the face. Turntimber Symbiosis digs a respectable seven cards deep for 4GGG which is doable for green decks and most importantly has built in insurance by putting counters on any 3CC or less creature you grab with this - which makes picking a utility creature totally fine. Also, some beautiful art on this one.
Testing Skyclave Apparition - This is not a Banisher Priest variant. It hits permanents. This is a big upgrade. Nice Sylvan Library, here's a 2/2 (if you get rid of me). The X/X token might turn out to be too troublesome, but I'm thinking more often than not, it will be worth it. Bloodchief's Thirst - Initially was a bit turned off by the sorcery speed. Thinking now though that the flexibility of being either an early game Fatal Push or a later game Never from Never // Return for 1 more all in one card might actually be good enough. Skyclave Shade - A recursive beat stick that can be either a 3/1 or a 5/3 each time you cast it. This is a flexible threat that keeps coming back for more. This is a harder slot to find cuts for, but this is worth a test. Agadeem, the Undercrypt // Agadeem's Awakening - Probably the second best of the MDFC's. There are suggestions that all of the mythic MDFC's are auto-includes and I don't find that to be true. There is a lot of opportunity cost involved with these. They take up cube real estate over more efficient spells and they often will require you to draft them over another viable option. The overriding question for me is if the spell is strong enough factoring in the land option to justify its inclusion. A fair spell with a land option is a good card. A bad spell with a land option is a fair card. Even with the triple black in this spells cost. A land that can also recur a single aggro creature straight to the battlefield for 1BBB or bring back a suite of creatures at 4BBB is quite strong. The cut for this is hard. Nullpriest of Oblivion - Child of Night with menace as a floor? A Zombify kicker that puts two bodies on the battlefield? This plays well at multiple stages in the game and provides a late reanimator backup. Kazandu Mammoth // Kazandu Valley - Remember when five power four drops were the cream of the crop? Blastoderm remembers. If you can "somehow" manage to trigger landfall in green, this is a 3CC 5/5. Off of an elf this beats for 5 on turn 3. It also curves right into The Great Henge (w/ Landfall). Also, it can be a land if you just need to smooth out your hand. Only downside here is the lack of trample, but this might be good enough as is. Inscription of Abundance- I continue to look for green non-creature spells for cube and this is a promising option. All of the modes are helpful individually and work well in combination with each other when kicked.
Watching Sea Gate Stormcaller- Snapcaster Mage this is not. That said, it can still generate a good amount of value for 3-4 mana. My biggest issue here is that between the CMC restrictions and the lack of flash, the pool of spells for this to copy is a bit small. Seems a little bit too much of a "if this and this and this come together" type of card for me to want to test this, but I will watch to see how it is performing. Shatterskull, the Hammer Pass // Shatterskull Smashing- I'm watching this one based on initial reception alone, my own evaluation of the card is that the spell side is too inefficient to justify running a land that bolts you or causes a loss in tempo. Magmatic Channeler - This card is getting a lot of hype. This is a very good impulse effect and I don't see it as card disadvantage so long as you're using the ability correctly. In a spells matter deck, this card is very powerful. I'm just not sure if it has enough general appeal outside of that shell. Crawling Barrens- I think the cost will make this too slow to be impactful. I do like that you can pump without animating, I hope WOTC continues to experiment with this area.
Summary
ZNR is shaping up to be a good cube set, but almost entirely in ways that are not consistent with the themes of the plane. Most of the land/X type cards we've seen so far appear to be under-powered despite their flexibility. Not a single landfall card is on my list as of yet, and most of the definite inclusions are aggressively costed generic effects (+1/+1 counters, permanent stealing, O-Ring on a body, etc.). Only kicker, which isn't a Zendikar specific mechanic, is represented among the cards currently being included or tested. On the other hand, this set is going a long ways to improve slots that were sorely in need of improvement.
Verdict is still out, need to watch some more. Also, yes I know that Day 1 standard with ZNR doesn't necessarily predict performance in cube, but it is better than nothing.
MH1 (18 inclusions) was a monster of a set largely due to the Canopy land cycle and the talismans. ELD has 13 inclusions for me and none are land cycles.
Stonecoil Serpent
Gilded Goose
Once Upon a Time
Bonecrusher Giant
Brazen Borrower
Murderous Rider
Oko, Thief of Crowns
Questing Beast
Rankle, Master of Pranks
Embercleave
Garruk, Cursed Huntsman
The Great Henge
Likely In
Luminarch Aspirant - A free +1/+1 counter wherever you want on each of your turns is huge value. Works great in aggro/tempo and isn't a poor late game draw either. Also a human, which is huge for those running Champion of the Parish.
Jace, Mirror Mage - Seems to be about on par with Jace Beleren, but infinitely more interesting.
Thieving Skydiver- Great tempo card, but that steal a mox, steal an equipment (not you Skullclamp)ability is what makes this a shoe-in for powered cubes and still a strong option for unpowered.
Nighthawk Scavenger- Nearly a strict upgrade to Vampire Nighthawk. Easy swap for those running that and probably better than some of the options people are running over Vampire Nighthawk.
Kargan Intimidator- The only other cubed red 2-drop threatening 4 damage on turn 3 is Bloodrage Brawler and discarding a card is a steep price for aggro (less steep if reanimator is part of the gameplan). This threatens 4 damage, can turn off a blocker, can trample over blockers, and may have incidental warrior synergies.
Turntimber, Serpentine Wood - The best of the MDFC's by a lot. The mythic cycle allows players the option to negate the loss of tempo when an untapped land is needed by taking a bolt to the face. Turntimber Symbiosis digs a respectable seven cards deep for 4GGG which is doable for green decks and most importantly has built in insurance by putting counters on any 3CC or less creature you grab with this - which makes picking a utility creature totally fine. Also, some beautiful art on this one.
Testing
Skyclave Apparition - This is not a Banisher Priest variant. It hits permanents. This is a big upgrade. Nice Sylvan Library, here's a 2/2 (if you get rid of me). The X/X token might turn out to be too troublesome, but I'm thinking more often than not, it will be worth it.
Bloodchief's Thirst - Initially was a bit turned off by the sorcery speed. Thinking now though that the flexibility of being either an early game Fatal Push or a later game Never from Never // Return for 1 more all in one card might actually be good enough.
Skyclave Shade - A recursive beat stick that can be either a 3/1 or a 5/3 each time you cast it. This is a flexible threat that keeps coming back for more. This is a harder slot to find cuts for, but this is worth a test.
Agadeem, the Undercrypt // Agadeem's Awakening - Probably the second best of the MDFC's. There are suggestions that all of the mythic MDFC's are auto-includes and I don't find that to be true. There is a lot of opportunity cost involved with these. They take up cube real estate over more efficient spells and they often will require you to draft them over another viable option. The overriding question for me is if the spell is strong enough factoring in the land option to justify its inclusion. A fair spell with a land option is a good card. A bad spell with a land option is a fair card. Even with the triple black in this spells cost. A land that can also recur a single aggro creature straight to the battlefield for 1BBB or bring back a suite of creatures at 4BBB is quite strong. The cut for this is hard.
Nullpriest of Oblivion - Child of Night with menace as a floor? A Zombify kicker that puts two bodies on the battlefield? This plays well at multiple stages in the game and provides a late reanimator backup.
Kazandu Mammoth // Kazandu Valley - Remember when five power four drops were the cream of the crop? Blastoderm remembers. If you can "somehow" manage to trigger landfall in green, this is a 3CC 5/5. Off of an elf this beats for 5 on turn 3. It also curves right into The Great Henge (w/ Landfall). Also, it can be a land if you just need to smooth out your hand. Only downside here is the lack of trample, but this might be good enough as is.
Inscription of Abundance- I continue to look for green non-creature spells for cube and this is a promising option. All of the modes are helpful individually and work well in combination with each other when kicked.
Watching
Sea Gate Stormcaller- Snapcaster Mage this is not. That said, it can still generate a good amount of value for 3-4 mana. My biggest issue here is that between the CMC restrictions and the lack of flash, the pool of spells for this to copy is a bit small. Seems a little bit too much of a "if this and this and this come together" type of card for me to want to test this, but I will watch to see how it is performing.
Shatterskull, the Hammer Pass // Shatterskull Smashing- I'm watching this one based on initial reception alone, my own evaluation of the card is that the spell side is too inefficient to justify running a land that bolts you or causes a loss in tempo.
Magmatic Channeler - This card is getting a lot of hype. This is a very good impulse effect and I don't see it as card disadvantage so long as you're using the ability correctly. In a spells matter deck, this card is very powerful. I'm just not sure if it has enough general appeal outside of that shell.
Crawling Barrens- I think the cost will make this too slow to be impactful. I do like that you can pump without animating, I hope WOTC continues to experiment with this area.
Summary
ZNR is shaping up to be a good cube set, but almost entirely in ways that are not consistent with the themes of the plane. Most of the land/X type cards we've seen so far appear to be under-powered despite their flexibility. Not a single landfall card is on my list as of yet, and most of the definite inclusions are aggressively costed generic effects (+1/+1 counters, permanent stealing, O-Ring on a body, etc.). Only kicker, which isn't a Zendikar specific mechanic, is represented among the cards currently being included or tested. On the other hand, this set is going a long ways to improve slots that were sorely in need of improvement.