People would have said the same thing about the likelihood of having a gay president 15-20 years ago. Instead, we had an openly gay and married presidential candidate, Pete Buttigieg, do quite well in the last election with his homosexuality not being a major point of the conversation.
The amount of progress on gay rights and the public's perspective on LGBTQ rights has been extremely fast. I think (and hope) that you are wrong and that society will be ready for a trans president much sooner than you anticipate.