There was a throwaway line in "Doctor's Wife" about a time lord that changed genders along with The Master so the seeds have been planted. And, honestly, I think fandom would stop clamoring for it if people would stop making stupid comments like this. I mean, I would love to see it, for the fun of it, but when you tell me I CAN'T? Oh now I DEMAND it LOL.

I mean, seriously, he is supposed to be out of regenerations anyway, according to the original canon, right? This show has rules, but they are pretty wibbly wobbly so I don't find a female doctor to be that much of a stretch.