If a doctor deems that someone should or needs to have gender reassignment surgery, why do we care if it's covered?
Why is that different from other medical necessities?
Any Joe Schmo won't be able to walk in and just have a gender reversal surgery at our expense that easily. They still have to prove it's necessary like with everything else, and you can't do that easily.
Any responsible psychiatrist would, in my opinion, wait a good deal of time before prescribing surgery as a fix.