Personally, the whole point of Doctor Who has been about change. Writers have changed, stars have changed, sets have changed, crew, showrunners, all of 'em.
Should the Doctor forever stay a male? I don't really care. But if he did turn into a female, I wouldn't have a problem. As long as they don't shoehorn stuff like girls being treated in an inferior manner (Mind you, I'm no misogynist, but I hate it when they shove it down our throats that women are being oppressed when relative to older times, they clearly are not.), I am totally on board.
"Freaking. Hiya." ~Bomeric"Freedom is the right of all sentient beings."