By which I mean that I'm OK with them if it's not a retcon. Anything is possible now, and it wouldn't be any more... disruptive? than Primaris.
There, I have pissed off both side of the FSM debate.

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By which I mean that I'm OK with them if it's not a retcon. Anything is possible now, and it wouldn't be any more... disruptive? than Primaris.
There, I have pissed off both side of the FSM debate.
Is there any technical reason lore-wise that makes FSM out of place? I can't remember anything specific. Although, I'm not the greatest expert in the deep 40k lore.
Outside of lore being completely in the hands of the writers... Technically and in universe, you need them male chromosomes or something to make Space Marines.
...which means you could still have FSM via regular SM who done gone transed their damn gender.
Must they be male chromosomes, though? As I understand, the Gene-Seed is somehow based on the Emperor and Primarchs and constantly improving, but does it actually contain gender info there? Like, who cares about gender on the battlefield in 40k?
See, that's the thing with the fluff: you don't need to argue about it from within the universe as we, the people outside it, have complete control over it.
As for how geneseed is in the fluff... I don't know what's the crucial male component in it, but I do know that it is not, in fact, constantly improving :D
With all the primaris business it's even a good time to change it, just say cawl fixed it like he fixes everything else.
I'd be a very happy clam if I next woke in a world where instead of primaris, we got true scale resculpts of existing models and female head sculpts, and a massively cut down unit list.
Then I'd get mad again cos the rules would still suck lol.