Having some doctors of new and interesting ethnicities would be interesting (although you'd, I think, lose something if they weren't essentially British at heart), but I'm a staunch opponent of a female Doctor. You can't gender-swap the role and have it still be the same character. I'd love to see more female Time Lords, I'd be there in an instant for The Further Adventures of Romana, but outside of Elseworlds tales and comedy specials the Doctor should remain eternally male.