I wonder who the black actor was that's been referred to several times as being under consideration for – but having never got – the role. And, yeah, I'd happily see Paterson Joseph as The Doctor. Or Hayley Attwell, for that matter, as per the suggestion further up this thread. Quite a few of the other usual suspects don't really seem right to me, though, or don't excite me. Richard Madden, Richard Ayoade, Olivia Colman… I've enjoyed them at various times in many roles – especially Colman – but for The Doctor? Hmm.
I see Tony Head's all over the news, too, about this. No chance there, I imagine. (He'd make an interesting Master, though, if that role was switched up again. I'm sure we can all pretend School Reunion did not exist.)