Hayley Atwell from Agent Carter fame (Captain America's WWII era love interest who founded SHIELD with Howard Stark) just threw her jaunty 1940's hat into the ring to play The Doctor.
Before Peter Capaldi took over as the time traveling alien, there was a growing movement amongst Whovians to find an non-white male actor to play the role. While Capaldi has proved his mettle and has still got some time left in the TARDIS, it doesn't hurt to know Ms. Atwell is hanging in the wings. That is, of course, if Marvel will ever let her not be Peggy Carter.