1. The twelfth doctor will never be a woman. His given sex is a male, just as River’s given sex is a female. Male timelords regenerate into male timelords and vise versa
2. Benedict Cumberbatch will never be the doctor, he has publicly stated in an interview that he will never be on Doctor Who. See https://www.youtube.com/watch?v=rGd-cuoIR0A @ 3:19
The first is not actually true.. in the episode Doctor’s wife, he talks about a friend who had a tattoo “Didn’t feel like himself without the tattoo. Or herself, a couple of times. Ooh, she was a bad girl!”.. although, I honestly hope that never happens..