I think when us cis writers try writing these 'gender plague' stories we think we're being really radical, real feminist, real profound when in reality we're being none of those, and also by this point it's just an antiquated trope.

The thing is that cis people are all transphobic--we've been raised with transphobic ideas, absorbed through family or cultural attitudes. We are NOT equipped to explore this 'thought experiment'. We're going to miss something incredibly transphobic in our thinking.

Even if you think your book is just so feminist or whatever, you're uh... still baking the mass death of trans people (usually trans women) into your core premise (and also, frequently, erasing NB people).

When your book codes trans suffering into its themes and world, you're going to have to ask yourself why that is and what you're trying to do exactly (and what that's going to look like to other people).

A lot of writers like to say 'the transphobic character is supposed to be an asshole!' but their books happen to be the gritty grimdark kind so the majority of characters are transphobic (or bigoted in other ways). You've chosen to populate your book with mouthpieces for bigotry.

Which is like, a choice you consciously made. (Not even getting started on how it's hack writing to show someone's villainous by making them a bigot. It's really utterly trite.)