I think there is a difference between biologically being more masculine or feminine in appearance/behavior, and wanting to change your biological sex.
"The day after Thanksgiving is, in my opinion, the biggest shopping day of the year." -
Peggy Hill
Transgenderism is a mess that ignores the biology bit and takes a drastic step in trying to change the way they appear to solve a mental issue.
I mean, kind of the whole thing with many trans people is that they are reacting because of their biology - we are still exploring just how much impact biology and physiology have on transgenderism, as there's input from hormones and the brain that we still don't fully understand. Most likely a lot more biological issues I am ignorant of as well. But I am not one to get bogged down in reducing transgenderism to biology - you can read my delightfully written and informative post above!
Also, gender dysphoria is a recognised issue - not all trans people go through gender dysphoria, and some have varying degrees of it, but it is a recognised problem that does affect the lives of many and cannot simply be resolved by a) ignoring their body or b) conforming to what others expect of them.
Because of its promotion in the mass media, many impressionable people (and most importantly children) are coming to believe that they should surgically alter their sex in order to solve their problems of not being traditionally masculine or feminine.
It's kinda as if a wider and freer understanding of gender, as is natural with social liberalisation, has resulted in greater self-understanding for many. And indeed, this understanding has provided an answer for many people who didn't know how to articulate their feelings and what they've felt inside! Now, as for children, that is entirely up to the parents and how they want to deal with that. If they believe/support their child, and have the resources, they'll be in contact with a doctor who will know far more than you or I about what is right for the child's wellbeing when gender issues are involved. They could even just decide to let things, you know, run their course and see what happens. If not, the child will grow up and formulate their own plan in life.
Promoting less restrictive ideals on gender is not a bad thing, like, at all.
The problem with this is that they will always be their birth sex, regardless of whether they get surgery or use hormones, because they cannot change their cellular structure significantly enough. In the past, a lot of these people would just be masculine lesbians or feminine gays and learn to be happy with their lot.
I am pretty certain that the only people who genuinely care about the cellular structure of trans people are a) doctors who rightfully need that information for medical treatments and b) people who are searching for more and more reason to justify their transphobia. I genuinely cannot think of one person in the trans community who feels incomplete or whatever because their body has the incorrect karyotypes or some shit. That may simply be anecdotal, but I mean... Peggy, really.
Next, transgenderism is not a modern invention or whatever. The definition? Of course. Our understanding of gender? Naturally going to be different compared to 50, 100, 1000 years ago and so forth. But it is woefully naive to think transgenderism solely a product of modern times. We can stretch back to Elagabalus if you want a real throwback to historical talk about gender transgression. As for the comment about masc lesbians and femme gays... I'm quite content to just let that sentence rest and let it speak for itself.
I think as masculine and feminine gender roles become more relaxed (although the opposite seems to be happening), there will be less transgenderism because of what I discussed.
Your whole post seems to have been 'the rise of transgenderism is TOO MUCH' so I'm not quite sure where you got the conclusion that it will decrease in the future, but good on you for surprising me.