I'd love to be able to see 20 years into the future to find out where all the trans stuff has gone. What will be the prevailing ideology then? How many of the under-25s who are calling themselves, or being identified by parents, as "trans" now will be living as the opposite sex, still be taking hormones, have had surgery? Will there be a huge amount of medical and surgical interventions to try and reverse the effects of "transing" treatments being doled out now? It did occur to me, watching the documentary last night, what a great money-spinner the whole trans industry must be - especially in the USA and other countries with no NHS. .
I think it'll be a mess, to be honest.
Some of the people who were transed but would have been happy as gay people will probably just stick with the surgicalized bits-added/bits-cut-off bodies that they now have, because trying to transition back is just too shaming/traumatizing, and because of the medical difficulties of actually transitioning back properly so who knows what your poor old body will look like in the end.
Some will transition back, at enormous psychological cost, and be angry and bitter about what has happened to them.
There will almost certainly be a lot fewer butch lesbians and femme-y gay men--which means probably somewhat fewer gay people in general. Not that this will represent a problem for GLAAD, Stonewall and all those organizations, since their focal interests and membership will be largely focused on "queer" people (trans of various types, heterosexual women who claim that they are "queer" because they are polyamorous or pansexual or pancake-sexual or .... ugh, who fucking cares....).
People who actually are gay will probably wind up splitting and forming their own organizations (amidst the usual death threats, rape threats, censorship attempts and so on).
People who have been transed and are now regretting it will sue in some cases. Some doctors may start getting more cautious, leading to more lawsuits from young people on the other side, who want to be transitioned.
Commentators will be writing articles on "The Great LBGT Split: Could it have been prevented?" and getting nostalgic for the good old 1990s when we were all in it together.