Judge Death wrote:
Someone completely unexpected (by me, at least), which is what happened with the last three.
Yup, that'll be about the size of it.
This. I had no earthly idea who Matt Smith was before he turned up wearing David Tennant's suit, but damn if he didn't own the role. As for what characteristics I'd look for, I think that the most important trait is the ability to be both whimsical and show the kind of world-weariness that belies the apparent age of the actor.
Oh, and there's zero chance that the next Doctor will be played by an older actor.