So, it is many thousands of years from the current age. Emrakul, finally awoke from her sleep in Innistrad's moon, starts her final attempt to twist all worlds according to her image, to devour all planes of the Multiverse.
As she started her crusade, she encountered forms of life unknown to her, forms that was not as easy to crush or subdue as mortals from ages past. Forms found across countless planes in countless numbers, ever speading, and driven by desire to spread. Forms united by one purpose, one supreme will, spoken by five eternal leaders, and one peculiar body feature - black, oily, infectious blood.
Phyrexians. They rediscovered technology of interplanar travel, and quickly converted dozens of planes by simple diplomacy or diversive operations committed by sleeper agents. A lot of planes that were not persuaded or tricked into global phyresis were conquered by ruthlessly efficient war machine. Infestation spread across the multiverse quickly, and some said that the Greatest Work is coming to it's end.
But some planes also have designed technology for interplanar travel - Ravnica and Alara among others. Those technologically advanced worlds predicted the threat of Phyrexia's return, and have taken cautionary measures. They fought, they fell under relentless onslaught of corruption, they surrendered. They could only hope to survive united. And only one leader could rule over such a vast union, only one person could have enough skill to run it, and enough ruthlessness to wage a war against Phyrexia.
I am, of course, talking about Nicol Bolas.
Now three forces fight over the Multiverse - Planar Union, the new Phyrexia, and the horde of Emrakul. To be an uncorrupted planar in such times is to be one amongst untold billions. It is to live in the immensely cruel and bloody regime. These are the tales of those times. Forget the power of arcane magic, for so much has been forgotten, never to be relearned. Forget the promise of progress and understanding, for in the grim dark future there is only war. There is no peace amongst the planes, only an eternity of carnage and slaughter, and the laughter of thirsting Emrakul.

So.
Comments?

You're missing Marit Lage.

Honestly though, this breaks everything that is Magic. Planeswalkers are at the core of the brand because they are among the few who can travel across the planes. Those uniquely identifiable planes fuel each new expansion. This throws that all out the window for an "everything but the kitchen sink" conflict.

As a "What If?" starting point for an original work of fiction? Sure, you do you! As the premise for a Magic expansion? No.

I was thinking about Warhammer 40000.
(I thought that the last paragraph was a clear sign)
Maybe it is a poor taste, but I like conflict kitchen sinks !

"You're missing Marit Lage."

She may represent a small faction, that can be a Chaos substitute.

Emrakul can be viewed as a Chaos substitute too, with all her cultists and mutations, but she also commands Tyranid-like horde.


I expected more interested people...
For me, it sounds like a cool idea.

I was just going to say "Warhammer: The Gathering" before I saw your last post. The big fun of 40k though, is all the different factions, each with a compelling reason why they should be the winner. You're a little low on factions to do the 40k thing, and the planar union guys don't seem to have much of a chance.

1) I tried to come up with more factions, but... for this I ether should come up with 100% original stuff, or borrow things from this site's expanded multiverse project, that I am not that familiar with.
2) At least Planar Union and Phyrexia can have a lot of subfactions.
3) Imperium also don't seem to have much of a chance - it is falling, slowly but VERY surely. And Orcs - they are just absolutely unorganized. And Chaos - it is not too focused on winning, more on trolling and fighting with itself. And Necrons - they are super OP, but just local threats. And Dark Eldar - scavengers and parasites that probably cannot survive without ones who they feed off. I would say that only 3 factions have good chances in the long run : Eldar, Tau, or Tyranids. Probably, leftover humans will ally with either Eldar or Tau, once Imperium will fall, though. Tyranids got the highest chance, tho.

Of course, I do not count for any extraordinary events: anyone finding undamaged STC, or Emperor awakening, or fifth God being born...

EDIT: I corrected my mistake: if ANYONE will find STC, not just humans, it will turn the tide in a wildest way possible.

Besides, Space: the Convergence is already (kinda) a thing.

Nice premise. I doubt Emrakul will continue to destroy planets/universes though. If her brief talk with Jace is anything to go by, when she gets out she will probably start creating planes again.

All she "said" was a big wtfwtfwtwtf thing that can be understood in 30 diffrent ways.

As an AU type of thing, sure, I say write around with that if you want to for fun. Personally, it has little draw for me because I really don't find those dystopian hell-futures enticing or fun. It's why I enjoy the Fallout games but LOVE the Elder Scrolls games. Things don't have to be Kaladesh bright, but utter "there's nothing left!!" isn't fun for me.

Fair enough, not all the 40k factions have a shot at winning. Dark elves are screwed. Necrons cannot advance, only decline. But most of them have a real shot. The orks are the most powerful faction in the galaxy, and if they ever did truly unite victory would be theirs. Chaos is basically hardwired into the universe itself, so in a sense they can't lose. The tyrannids are ruthlessly efficient, expansive, and likely numerous beyond all life in the Milky Way. Humanity has a whole big mess to untangle if they want a shot at keeping the title, but they are the reigning champ and will continue to be for the foreseeable future. The Tau have all the empire's best features without the crippling flaws. The Eldar are greatly diminished, but their long term goal of slaying a god actually seems feasible.

As for Magic:40k factions? I think that grouping all the miscellaneous planes together was a mistake. Give Bolas his empire, and make it the biggest nonPhyrexian, nonEldrazi faction, but don't give him everything.
Do a Gatewatch-type faction. They're smaller than the Bolas empire, but have the most planeswalkers (because they're the only faction that anybody would willingly choose). The Gatewatch refuse to give up their principles and submit to Bolas. Bolas is all like, "Surrender and the super evil factions won't win. I'm sort of tolerable". The Gatewatch is all like, "No. None of the evil people get to win. We'll wait until you're desperate enough to ally with us". Bolas is all like, "Let's be reasonable. The Gatewatch says, "Stop being a jerk". And they recognize that they're both better off focusing their energies on the real threats than destroying their potential ally/resource.
Season the mix with one or two other holdout factions (The Rabiahs? United spirit realms of various planes?).
Then just split up the Eldrazi and Phyrexians into cool subfactions and I think you're good to go.

1) Orks are indeed a biggest factiOMNOMNOMNOM oops, they aren't.
2) Chaos can't lose in a straightforward conflict, but also can't win in it.
3) I imagined a different reason Eldar can possibly win - their technology, lore, and genome (that can be used for augmentations and, perspectively, regular reproduction.)
They currently have no resources to benefit from them... and cannot really ally with humans, because they (and humans) are huge xenophobes, racists and traitors. But after Imperium will fall, and Eldar will be on the brink of extinction, their illusions of grandeur will break.
4) There is no need for Bolas to make his empire a dystopia. He is super power-hungry, but probably will not be a prick once he will gain his power. He will even somewhat suppress his nasty nature to preserve popularity, since popularity is power on a scale that large.
5) Things he will maybe do as supreme leader:
1. Establish mandatory torture for all citizens at 18th birthday (depends on race) to reveal their hidden sparks.
2. Install kill-switch in all government and military figures.
3. Zombify all the dead. Too important resource to waste, right ?
4) A lot of reasons for planeswalkers to join Bolas. White like order and tyranny, blue want to research technologically advanced faction, Black sees in it a highest chance for survival, red characters who like to effectively fight for fun, and green characters who want to effectively fight for preservation of nature.
5) Gatewatch faction... Again, Planar Union is not an all-out dystopia. I see them more as a Rebel faction, which White characters join because they want Bolas to die, Green characters join because they dislike "unnatural" technological Union, and other join because they value freedom more then knowledge, safety, or war.

I just don't see any real flavourful hook for the Bolas empire. What's the flavourful connection? You're throwing away all these awesome, unique planes without getting much in return.
Did the orks suffer some major catastrophe? They used to have the most sheer power of any faction.
And though Necrons can never gain in power, they have yet to reveal their true numbers. Also, the only reason they went into hibernation is because they were successful in their last galactic conquest. They could win, they just couldn't last forever. And if they won, it would actually be the end of chaos.

They are bigger then tyranid vanguard. When tyranid rearguard will join the party, they will die first.

Imperium is only vaguely an empire. One world is super different from the other.
In fact, ANY planet is welcome to Imperium, as long as it
1) Pays a tax (it differs)
2) Keeps Psykers under control, and gives them to Black Ships.
3) Has somewhat Emperor-worshiping somewhat state-religion.
4) Does not deals with Chaos, and does not deals too much with Xenos.
Yes, that's all for the rim. All totalitarian s... is largely limited to Segmentum Solar.
So is Union. Death Corps of Grixis are vastly different from Dominarian First and Only.
Planes are still unique.

Flavorful connection is
1)Armies of planes fight together
2)All governments answer to Bolas, and execute his decisions.
3)400% of paranoia and witch hunts.
4)Cults of Emrakul, Sleeper agents of Phyrexia, spies of Gatewatch, etc.
5) Interplanar travel is aviailable.

What is more awesome: Theros Gods as leaders of independent Theros, or Theros Gods eldrazified, or Compleated Theros Gods, or Theros Gods, minions of Bolas ?
LOL

I think the core idea has merit (although I don't think it would be something that could interest me for a long time), but I think you could do more.

Having Bolas, Eldrazi and Phyrexians as the main factions is probably not a bad idea. I do think you should at least consider which of the current planes fit where.

As for the Theros gods, I had this idea: I think there are some planes that could probably withstand or at least hold out, against the big three. Theros is one of them. They already knew about all the possible threats because of Kruphix and could have been preparing for them. If you have readily available cross-planar travel, Theros could have created a coalition of planes that have some sort of advantage against either the Phyrexians, the Eldrazi or Bolas. Theros could withstand the Phyrexians, in my opinion, because Nyxborn probably can't be compleated. Same with Kamigawa and their spirits. Kaladesh might stand a chance against the Eldrazi because they don't rely on mana all that much.

I also think you can get away with creating two new Eldrazi titans. We don't know anything about how they are created, but there have been hints that they're simply a function of the Multiverse so it sorta makes sense that they Multiverse wants three of them at all times or something.