At first glance, you're running a ton of incredibly awkward win conditions for a deck like this. Door to Nothingness will very rarely win you the game if people know what they're doing, as they'll either hate it or you off the field before it gets a chance to untap. It's also rather unwieldy and slow for a wincon. The gates also aren't that great unless you literally want to devote your entire deck to making them good. If you need another wincon, try Purphoros, God of the Forge, especially since you already have Primal Surge in here.
One or two other things: a planeswalker deck like this wants to have some wrath effects in it, and they happen to go really well with your commander too. Also consider cutting Darksteel Forge; there aren't enough artifacts here to make it worth it. Overall, I think your deck is just trying to do a bit too much at once right now.
Door I run because it's kind of an inside thing in my playgroup that you have to run it if you run all five colors
I think that I can afford to run the gates seeing as I got the manafixing slivers as well as quite a lot of manastones. + the added benefit of saving a hundred or so bucks on the manabase (kind of on a budget, and I prefer to blow it on walkers).
But please do suggest more things to cut, I always struggle with it. I usually end up leaving a card in that used to fit the deck but I end up cutting everything it synergises with and forget it.
The gates aren't necessarily bad because of mana fixing, they're bad as a win condition unless you're going to go all out to support them because it's just way too slow, and you're not guaranteed to draw Maze's End at all during any particular game with this setup. If you're worried about budget, the Ravnica duals only cost 3-7 bucks apiece, and the Vivid lands cost less, and all of them are much better for this deck than the Gates are.
If you're going to be running DTN, you should probably look to add Voltaic Key and other such untap effects to your deck; otherwise you run a huge risk of the card getting removed before your turn comes around again. Plus, you get the added synergy with Nevinyrral's Disk, Contagion Engine, and other such ilk. Privileged Position also gives you more protection and synergizes well with Hivelord, making your Slivers almost unkillable. I think it's a bit silly that you're being forced to run a card that's fairly bad in multiplayer EDH if you use 5C, but that's none of my business.
As for other cuts, I would replace Dictate of Karametra with Mana Reflection; you lose flash and it costs a mana more, but giving everyone double mana leads to other players comboing off sometimes, so it's worth it. Eternity Vessel isn't a very good card, and it only gets worse as the game goes on. You could be running something much more powerful in its stead like Akroma's Memorial. Finally, the Obelisk and the Cluestones could be replaced with much more valuable things. Gilded Lotus is one that comes immediately to mind, Doubling Cube is another.
Lastly, consider running Sliver Overlord in your 99. It lets you tutor for basically anything you need to make your creatures better, and it also opens up the possibility of shenanigans with stuff like Unnatural Selection.
I need some help on what to cut though...
5 Door to Nothingness
10 Primal Surge
Planeswalkers (13):
8 Nicol Bolas, Planeswalker
6 Elspeth, Sun's Champion
5 Liliana Vess
5 Garruk, Primal Hunter
5 Vraska the Unseen
5 Jace, Memory Adept
4 Ajani Steadfast
4 Kiora, the Crashing Wave
4 Jace, Architect of Though
4 Ral Zarek
4 Elspeth, Knight-Errant
4 Chandra, the Firebrand
4 Gideon, Champion of Justice
Slivers (17)
1 Galerider Sliver
1 Striking Sliver
2 Gemhide Sliver
2 Manaweft Sliver
2 Quick Sliver
2 Two-Headed Sliver
2 Venom Sliver
2 Sentinel Sliver
2 Predatory Sliver
3 Blur Sliver
3 Syphon Sliver
4 Bonescythe Sliver
4 Vampiric Sliver
5 Pulmonic Sliver
5 Ward Sliver
6 Megantic Sliver
7 Groundshaker Sliver
1 Sol Ring
1 Expedition Map
2 Armillary Sphere
3 Chromatic Lantern
3 Darksteel Ingot
3 Obelisk of Grixis
3 Druidic Satchel
3 Boros Cluestone
3 Selesnya Cluestone
3 Gruul Cluestone
Value Guys (7):
2 Grand Abolisher
2 Imposing Sovereign
2 Gatecreeper Vine
2 Fog Bank
3 Athreos, God of Passage
3 Laboratory Maniac
3 Guard Gomazoa
Value Artifacts (8):
2 Contagion Clasp
3 Temple Bell
4 Nevinyrral's Disk
4 The Chain Veil
6 Contagion Engine
6 Obelisk of Urd
6 Eternity Vessel
9 Darksteel Forge
Value Enchantments (11):
1 Land Tax
3 Rhystic Study
3 Aura of Silence
3 Prison Term
3 Underworld Connections
3 Mind Control
5 Asceticism
5 Dictate of Karametra
5 Mirari's Wake
5 Sphere of Safety
5 Doubling Season
1 Command Tower
1 Sliver Hive
1 Mana Confluence
1 Transguild Promenade
1 Vivid Marsh
1 Vivid Creek
1 Crumbling Necropolis
1 Bojuka Bog
1 Temple of the False God
2 Forest
2 Plains
2 Island
2 Mountain
2 Swamp
Win-con Lands (12):
1 Maze's End
1 Thespian's Stage
1 Dimir Guildgate
1 Golgari Guildgate
1 Orzhov Guildgate
1 Azorius Guildgate
1 Selesnya Guildgate
1 Simic Guildgate
1 Gruul Guildgate
1 Boros Guildgate
1 Rakdos Guildgate
1 Izzet Guildgate
One or two other things: a planeswalker deck like this wants to have some wrath effects in it, and they happen to go really well with your commander too. Also consider cutting Darksteel Forge; there aren't enough artifacts here to make it worth it. Overall, I think your deck is just trying to do a bit too much at once right now.
IRL: Patron of the Moon
I think that I can afford to run the gates seeing as I got the manafixing slivers as well as quite a lot of manastones. + the added benefit of saving a hundred or so bucks on the manabase (kind of on a budget, and I prefer to blow it on walkers).
But please do suggest more things to cut, I always struggle with it. I usually end up leaving a card in that used to fit the deck but I end up cutting everything it synergises with and forget it.
If you're going to be running DTN, you should probably look to add Voltaic Key and other such untap effects to your deck; otherwise you run a huge risk of the card getting removed before your turn comes around again. Plus, you get the added synergy with Nevinyrral's Disk, Contagion Engine, and other such ilk. Privileged Position also gives you more protection and synergizes well with Hivelord, making your Slivers almost unkillable. I think it's a bit silly that you're being forced to run a card that's fairly bad in multiplayer EDH if you use 5C, but that's none of my business.
As for other cuts, I would replace Dictate of Karametra with Mana Reflection; you lose flash and it costs a mana more, but giving everyone double mana leads to other players comboing off sometimes, so it's worth it. Eternity Vessel isn't a very good card, and it only gets worse as the game goes on. You could be running something much more powerful in its stead like Akroma's Memorial. Finally, the Obelisk and the Cluestones could be replaced with much more valuable things. Gilded Lotus is one that comes immediately to mind, Doubling Cube is another.
Lastly, consider running Sliver Overlord in your 99. It lets you tutor for basically anything you need to make your creatures better, and it also opens up the possibility of shenanigans with stuff like Unnatural Selection.
IRL: Patron of the Moon