Even though it seems to be a popular speculation (among even Steven Moffat), I somehow doubt it will be any time soon. I wonder if any female actresses have tried for the part or if they themselves decided against it because of how they feel about the idea; that has never been addressed to my knowledge.
On the other hand, I think him being a dude is pretty okay any way you slice it. I mean, I'm not totally against it, but I have some doubts that anyone would be able to see it/utilize it beyond it being more of a gimmick. It would be fun/interesting to be proven wrong though. Also, don't get me wrong; I'm not against a female playing the part, and I don't have doubts that an actress would be able to do it, but there are a lot of other factors/people that would have to work out for it to be a successful move.
My phrase of the day is "I'm not against it," apparently.