Stephen Fry has the potential to be awesome in the role. If they should fancy going back to a Hartnellish Doctor - unlikely, I agree - then how about Richard Wilson?

He's around fifteen years older than Hartnell was when he took the role, so while he'd be good I imagine the shedule would be a bit punishing for a man in his seventies. I would like to see his Empty Child character get another guest spot, though.