I think The Doctor being a paternal figure is a very key element of the show's DNA that shouldn't be changed. A female Doctor could
work but there's a 99.99% chance the writers would just fuck it up so I'm not really up for it. I'm imagining how Moffat or RTD would write the post-regen scene of The Doctor examining her new female body and already cringing.
It's all a bit too New Earth for me.