Your gateway to endless inspiration
Some thoughts about a 30k/40k "Roleswap Heresy"
I know there's a "Dornian Heresy" out there and I'm certain I've seen someone's take on this concept where it was Guilliman who went 'Full Horus'. So assuming that it's a straight swap of who went Traitor and who didn't here's how I'd do things:
The Arch-Traitor role: The person who takes Horus's place in this hypothetical scenario.... I'm gonna go with Sanguinius for several reasons.
Khorne still doesn't get him this way.
The aesthetic of the fallen Angel turning on the Emperor.
We still get Horus Vs Sanguinius at the end of the siege of Terra.
Dante as Abaddon's equivalent in 40k.
Blood Angels taking the role of the Black Legion (The Black Angels?) In 40k, the go to Chaos Legion with followers of all four Gods in their ranks actually works surprisingly well....Death Company are Khorne Berserkers, the Blood Angels are a legion that degrades over time and that just feels like something Nurgle wants a piece of, Everything about the Blood Angels aesthetic and the way they're describing in the novels is just Slaanesh levels of pretty and of course they'd have winged librarian Dreadnaughts as a Tzeentch option.
Straight up Role Reversals: Because these feel like they have to be done.
The Iron Warriors and the Imperial fists would switch places....Which in 40k would mean that there's no loyalist Black Templars, at least not as an Imperial Fists successor.... Although I could imagine the role being filled by a Word Bearers successor Chapter.
The Dark Angels and the Alpha Legion....And still nobody knows which one is the loyalist. The potential for stories here would be great, because even here nobody would know where the Alpha Legions' homeworld was or where any of their successors were based; problems with the inquisition ensue.
The Four legions dedicated to the Gods:
Nurgle gets the Iron Hands - But only after Ferrus Manus dies.
Tzeentch gets the Space Wolves... and I can hear the hate coming but hear me out, it's another fun role reversal and their aesthetic lends itself well to a shamanic vibe and a style of play and general vibe that's Tzeentch but not in a thousand sons way...Hell the curse of the Wulfen could be their version of the flesh change.
Slaanesh gets the Ultramarines and this one feels right, of course the Primarch who literally wrote the book on what it is to be a Space Marine fell to the God of Excess.
Khorne gets.....And I'm gonna explain myself beforehand here. I've heard it said that if it wasn't for the Butcher's Nails Angron would have been the kindest Primarch and that he had the ability to take away the pain of others.....So I think it would be thematic to make the Salamanders Khorne's chosen Legion. They're the Burn in Kill, Maim, Burn and Demon Vulcan is a terrifying prospect.
Which leaves the White Scars and the Raven Guard to fill the roles of the Word Bearers and the Night Lords and funnily enough I could see both Legions working as a Night Lords equivalent in their own ways.