No way they'll do a woman... I just don't see it.
I think it's most likely to happen as a desperation move on the part of the BBC -- ratings are soft, the production is troubled, the audience isn't engaged, let's do something groundbreaking to get people talking again.
Wait. I've just described the current situation...
To be honest, while I'd like to see a female Doctor, I'm not sure I want to see Steven Moffat be the one to write and develop the first female Doctor. Though he would finally be in a position to slay the Bechdel Test Monster that has vexed his era if he had a female Doctor.