We agree about that, at least. They definitely aren't going to, the only "question" is why didn't they
I almost didn't post the following but meh, might as well. I don't feel upset, just thinking outloud.
It's up to each regiment, whether or not it's coed.
Yeah the worlds of the Imperium are countless (arguably literally, lol @ Ministorum) and diverse. The many feral and feudal worlds in particular are understandably unenlightened, even by the Imperium's grimdark standards. From what I've heard the Imperial Guard makes a point of standardizing the Guard tithe in many ways, like unit size, but keeps regiments divided by world to promote unit cohesion and a certain amount of unique tactical diversity. Also they actually speak the same language, a plus.
This also gave me a thought about the gender composition of the Imperial Guard. The text I was reading insisted that planetary governors tend to not only pay the full tithe, but send their best PDF soldiers. Apparently their greed is generally outweighed by their fear of drawing the Imperium's ire (or even its disfavor, since they rely on the IG to protect against significant foes).
I think we can agree that the strongest 10% of their armies are going to be disproportionately male. Since this is 40k, where melee is magically rendered relevant in all but the bluest conflicts, raw physical strength is as or more important than any other factors. So I conclude that Guardsmen are mostly male.
This doesn't apply to the aristocratic officer corp (upward mobiliity: still not a thing), or the commisars from the orphan-academy. Just the conscripted enlisted.
And maybe it applies to Space Marines, maybe it doesn't, I don't think it matters. I think the excuse that the geneseed "just doesn't work" is nonsense and could easily be noncanon. The real question is why bother? Do battle sisters really need to eat brains and spit acid, and act out the insanities of the primarchs? I say no. They're nearly as effective without all that, and substantially cheaper. Sure they're shorter and less strong inside their
powered armor. They still more than hold their own in close combat (either by fanatic swordplay or flamers). They don't have the sheer power and reactions of space marines, but they make up for it in numbers and Ecclesiarchal cohorts. And their fancy
daemon princess Living Saint.
We're in this situation because early GW was understandably macho (and silly), and they only dropped the silly part. That's alright, it's just worth acknowledging I think.
Lore-wise I think it's concerning that the avatar of humankind is excessively male and only wanted sons, but maybe that's a reaction to the Only War galaxy (which he's partly to blame for, with his xenophobic crusades).
Heck 3.5 of the ruinous powers are male too. Maybe this is sort of metaphysical commentary on the inherently macho nature of the setting
I think GW has come a looong way in making the setting deeper and less silly. The amount of women in positions of power is a sign of that. I really don't mind that the Imperium believes it can't make FSM, because the Imperium is incompetent and terrified of change. "Big E did it that way" is fine *even if he didn't actually*, heh. I wouldn't be surprised or unhappy if CSM started fielding FSM, though, if only to see the Imperium's reaction.