It should be clear as day to anyone with even a passing interest in biology. Once we've identified exactly what genes influence transgenderism, and genetic editing of our embryos is commonplace for the populace, no one is going to allow their children to be born with a predilection for being transgender. You'd be literally putting your child at an enormous disadvantage for no discernable reason.
Look how long its taken for gay people to be accepted by society. Not decades, but centuries. Transgender people don't have that long. In a century, we'll be editing genetically superior superbabies. No parents in their right mind would give their children such a tremendous disadvantage in life when they could make them "normal". I suspect gay people will probably go extinct too, but one never knows with 100% certainty how these things play out.
I suspect a great many classes of people / traits will go extinct. Down's Syndrome babies will certainly be screened out of the population, because again... in a society of beautiful 200 IQ super athletes, why would you deliberately hinder your child?