I am drawn to the 4MV reanimation spells, probably because my style of play. Is it not your experience that you have tight turns in the early-to-mid-game where you simply do not have the extra B mana to cast one of the 1MV spells to bring CoA back? This happens to me a lot. And those 1MV renanimation spells are terrible topdecks.
Before the rules change, I would have agreed with you. Back then, CoA could sit in the GY post wipe and of course, the 1MV reanimation is no good then. It didn't much matter if your yard got exiled, because then you could finally cast CoA from the Command Zone again. But anyway, that's in the past. These days there's little reason not to put CoA back in CZ after it dies and wipes (unless you have that cheapening reanimation in hand). So that means CoA is either on the battlefield or in the CZ and the 1MV reanimation is just more cost effective than 4MV reanimation then - but it's for that "next" wipe, rather than the current one at hand (which is, or just was, financed directly from CZ as per normal taxing rules).
There can be different advantages to either effect early game. If you drop CoA t4 and tap out, it's easier to have mana on t5 for reanimation AND sac outlet if you use the 1MV variant. If you play CoA t5 with one mana open to blow it up and you're forced to do that before t6, then the 4MV reanimation is better than just putting CoA back in CZ and paying 7 mana next time - despite the cheapness of 1MV reanimation, you just don't have the mana to do it all same turn that early.
All in all, I think Late to Dinner and Mistmoon Griffin are very playable cards in the deck, especially if you run Dimir House Guard with a few other solid 4MV targets. I would love for a 3MV variant to be printed as common, and it seems like WotC are sweetening the 4MV deal already - perhaps power creep will eventually grant us something like Breath of Life costing 1GB or 1WB (gold requirements makes it balanced IMO) so we can tutor it with 3MV transmutes. Until then, I will probably be running all three 1MV reanimation though.
Is there a workable version of the mana base that prioritizes untapped mana sources/lands? This could possibly work with Trinket Mage, as you suggested.
I think this was one of the most interesting questions asked about this deck in like a year or so! It sparked many ideas and I've given it lots of thoughts the last couple of weeks. I think we've been so obsessed with fixing, running enough sources, getting WUBRG with a pauper mana base etc. that we've missed the fact that we can afford to relax a bit and try to make a slightly faster mana base now that we have better fixing.
The obvious choice would be to run more basics and more panoramas. This is not unproblematic. We're already maxed out on dedicated blue sources IMO, so running more would lead to less WUBRG t4-5 and more redundant early lands. Black sources pose the same problems. We can add more basic forests, but those slots come at the expense of other green sources: Green sources that also tap for U/B gives us more colored mana for the spells we want to play and have lots of, and green sources that tap for R/W lets us fetch extra islands with green ramp spells rather than mountain/plains.
It becomes a philosophical questions: What do we mean by a fast mana base? Playing more Forest to have fewer tap lands might seem fast on paper, but will it feel fast when you can't play Counterspell on turn 6 due to lack of UU? Concretely, my observations these last days leads me to believe the following:
1) It is certainly necessary to play Glacial Floodplain, Rimewood Falls and Volatile Fjord in order to support Farseek, Into the North and Mystic Sanctuary, for all optimal manabases. Shimmerdrift Vale, while the worst of the "any lands", is also hard to avoid at present.
2) It is not obviously necessary to also play Arctic Treeline, Highland Forest and Woodland Chasm to support Land Grant (or any ramp spell at common with keyword "Forest", as I've explained earlier). This needs clarification. Obviously, Land Grant isn't such a good spell to motivate running three tap lands to support it. However, if the mana base requires running more green sources that ETB tapped anyway (see reasoning on basic forests above), a virtually free spell that tutors at 2MV to boot and can fix two colors at once, is not a bad card or a bad reason to pick these green sources in particular.
3) A separate question is the need for green mana fixing at the 2MV slot. The idea has been previously that we can have more keepable hands with a card like Mycosynth Wellspring or Land Grant, not only to these cards themselves but because we could theoretically tutor for them at turns 3-4 to get a green source even when we didn't have one in our opener. However, with the present mana base, it will be very unusual to have 3 mana and no green source. Furthermore, we probably can't expect to have 1BB (for transmuting Shred Memory) even under such circumstances, meaning only Dimir Infiltrator and Muddle the Mixture would feasible fit for purpose. That's only 2 cards, of which we'd need one in hand in addition to the strange 3 lands but no green situation. I have not done any math on this, but it seems very unlikely, and will probably only increase keepable hands with 1-2%. All in all, the tutorability of Wellspring/Grant should not weigh heavily into the decision of running them - they can be good cards in their own right though.
4) The conclusion of 3) above has opened my eyes to yet another fixing option: Jhessian Zombies. It costs 2 to play (to cycle) much like Mycosynth Wellspring, but cycles at instant speed. Much like Land Grant, it can find duals - but islands rather than forests, which is much better since we're already running those to support cards as per 1) above. Moreover, it can find Mystic Sanctuary, as well as basic islands and swamps that don't ETB tapped. Downside is costing 2 to cycle where Land Grant is free, and being untutorable (but it's no biggie, as explained above). Thoughts?
5) Returning to the original question of more untapped lands, it is possible to run only the three island duals in 1) and squeeze in green sources in ravnica karoos, panoramas and forests. I still recommend Bant Panorma for all mana bases at present - I think it's at least a good a green source as Shimmerdrift Vale. Jund Panorama is probably necessary if you're not running the forest duals in 2) and much better than running a third Forest IMO. Grixis Panorama is a good card for any deck that has enough green sources and wants another good non-basic. Esper Panorama is slightly worse and probably only worth it if you have many white cards in the deck, and Naya Panorama would probably need support from 3 forests and 2 mountains in the mana base before you should consider running it (there's just no room IMO). I like the karoo set of Azorius Chancery, Golgari Rot Farm and Izzet Boilerworks because it lets you fix all colors at card parity with Crop Rotation, while being redundant in blue - the most important color to have lots of and a needed karoo color to pull off combo. However, with cutting away almost every white card in the deck as I'm currently considering, you can squeeze another green source in there by swapping chancery for Simic Growth Chamber. You could run all four of course, but that's more tap lands for you. I'm not a big fan of Dimir Aqueduct mainly because it risks being both black and blue redundant early game, and because it's not a green source to help with further fixing from ramp either. Certainly playable though.
6) The artifact lands and Trinket Mage are probably a meta call as you say. There are very few effects like Obliterate where you can't counter the mass LD, so it will be a question of opportunity costs. Running a few indestructible artifact duals to support Trinket Mage is no worse than running a few forest duals to support Land Grant really. The question is how Trinket Mage compares to other staples like Sea Gate Oracle - if it can earn its own slot. Trinket Mage needs to be much better than Borderland Ranger in the deck, and the indestructible artifact lands alone do not accomplish that. Cards like Expedition Map and Nihil Spellbomb are not quite good enough to be staples in their own right today, but certainly contenders for open slots. Maybe Trinket Mage will be the card to tie it all together and make a synergy that's greater than its parts?
All in all, I now think there are three different "optimal" mana bases at present that should only differ in a few cards:
A) The Land Grant version with all the snow forest duals.
B) The heavy basics/panoramas version that plays as many untapped lands as possible. This could also support Far Wanderings if one so desires, or possibly run Jhessian Zombies.
C) The Trinket Mage version with a few indestructible artifact duals and some main deck trinkets to boot.
What I'm really waiting for is another "breakthrough" like the thriving lands cycle or snow land duals cycle. The days of Panoramas and perhaps even cards like Shimmerdrift Vale are probably numbered, the question is only how quickly land/fixing power creep at common proceeds.