I also think it's impossible to separate in most cases external influence from internal motivation
I know you said we're leaving trans issues out here to consider social contagion, but consider:
undoubtedly acceptance of trans people has lead to more people transitioning in some capacity, and will continue to do so
but since it was extremely difficult to transition - and often not recognized as transitioning - until quite recently, it's also very difficult to say whether there are actually more trans and gender nonconforming now than there were say, 50 years ago
certainly there are more people living openly, but how many people would have transitioned etc if it was more feasible
this gets back to what I mentioned above - as friction, both physical and (hopefully) social, decreases and perhaps also as it becomes possible to live in different kinds of altered or artificial bodies, how many people will choose to do that?
I don't claim to have the philosophy background that you or some other people here do, but I think this is some of what Donna Haraway was getting at in A Cyborg Manifesto - that these categories and boundaries are likely to eventually become on some level obsolete. probably the minute someone can figure out a way to make money making them obsolete.
That shouldn't mean that people who want to remain within those categories can't do so, tbc, which seems like the ultimate fear of TERFs