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.
Sexist or change-fearing attitudes in fandom need shaking up and our tragic, engimatic world-breaking travelling wizard can work as a woman just as well a guy.
Oh, alright then you've got me. Emma fucking Watson would be perfectly satisfactory, idiosyncratic casting for The Doctor. She'd likely be the best performer since Troughton in the role.
Perfect. Squee. Squee. Squee. ^_^.