[quote=Kaga]
No, it's been implied that regeneration can change a Time Lord's sex. I believe it was in the episode "The Doctor's Wife" when the Doctor was talking about a Time Lord he knew once and reminiscing about their adventures - he referred to them as "he" most of the time but at one point he said "or she, in one regeneration" or something similar. I don't remember the specifics but I'm certain it came up. Additionally, immediately after the Doctor regenerated into Eleven, he momentarily thought he might've become female after realizing how long his hair was. I don't know if it's a good idea for the Doctor himself to regenerate into a woman at some point, but it is canonically possible. If they do go that route, they'd probably add to the lore saying it's rare for a regeneration to do that, since it's never come up before except in those two instances (that I'm aware of). Now that I think about it, I wouldn't mind a female Doctor coming in similarly to how the War Doctor did - not taking up entire seasons but just one movie or special. That's probably the best dose at which to deliver something so different.
[/quote]

I remember this, it was whatever Time Lord was represented by the snake eating its own tail. 

Personally, Moffat just seems too timid to push the Doctor into any light that break them off standard media image. Who is all about the potential of humanity and how we can push ourselves to be the best we could possibly be. I don't think a female Doctor should be considered so radical that it should be railroaded into an obviously brief appearance. I mean, really, does genitalia make any difference by this point? The Doctor has flirted with other male-bodied characters and had 'intimate contact', so, what could possibly be so radical about this?

I think a woman Doctor would make sense for the path the show is now taking. They talked about Twelve being a more paternal figure rather than the possible sexual tension thing that's happened since '05. That shows the want to do something a little new. Something a little different from the trend we've established thus far and I'd welcome a Doctor reminiscent of Melody in her second regeneration. Actually, Melody's most common regeneration is a fantastic example of what the Doctor could be too. I honestly don't see the difference sex would make for a show that's lasted the test of time and everyone knows may change the protagonist in as little as a year.