But in the end, it's still 'because I said so' + money. It's going to be like the California Medical Marijuana Law, anyone with $75 bucks can buy a diagnoses and get the card, the doctors will even 'suggest' (more like 'prompt') the correct thing to say (which turns out to be just about anything).
The reason the Feds don't care about it, is because 'your current gender' does not matter to them, and they have all the information they need (and a lot more) anyway.
And, while some states might have a higher standard, others do not, any Federal law is going to written to the most regressive standards, not the most progressive ones. As it is, changing the requirements for passport stuff is a matter of re-writing some administrative standards and publishing those changed in the Federal Register, what you are proposing is something that would take an actual law. So that means that Congress would write it and debate it, and you are going to get something written by Steven King and Michelle Bachmann and Sam Brownback and the new standard will be along the lines of "you can change your gender when (our) god says it's OK."