There's a disturbing amount of misogyny in this thread. Why the fuck would casting a woman automatically make the show campy? That's absurd. And why someone would take my joke about Catherine Tate seriously is beyond me...
Sounds like making excuses to me. "Oh a female doctor could be ok" but then looking for reasons to decide it wouldn't work. The writing would be awful, they'll case an unsuitable actress etc etc.
With Moffat the writing probably would be awful. Look up his comments on how hard it is to be a middle class man and be prepared to cringe. I like Moffat's writing but the dude has some really serious sexism issues.