In 1986, the producer largely responsible to bringing the character to TV in 1963 recommended to the BBC that a future version of the Doctor be female. In 1999, the novel Interference - Book One explicitly mentioned Time Lords changing genders, and there's been fanon for decades assuming that it could take place. So it's hardly a new development, it's been one that just hadn't made it to screen.

Saying that because they didn't mention it meant it didn't exist is roughly akin to saying no one in Starfleet has to take a crap because they never showed a toilet on the Enterprise.