It's not transphobic to question whether a women-only organization should include transwomen. It's a legitimately hard question with no 100% correct answer. You have to deal with the possibility of people who identify as female according to their own standards, which you might consider dishonest or confused.
Step off it, mate.
There is a correct answer: People who call themselves women are women. Simple as that.
You're not the arbiter of Gender.
So Trump can be the first female president... if he wants?
Sure. Trump's an abhorrent human being but that doesn't stop me from respecting their gender identity.
I don't go around misgendering people I don't like because I don't like them. That's shit.
I suppose it's something that would get addressed if a problem arises. But for now, why bother creating a whole plan to solve a problem that doesn't actually exist?