No idea who (sorry) she is.
Back in the 80's this would have been a bigger deal I think.
Besides they have been leading up to this for white a while - a female Master, a Time Lord General who changed from a white male into a black female, plus a few side comments from the Doctor not remembering if he was a man or a woman in his early life.
I say its less who the actor is and more of how the stories are. Smith and Capaldi were both great Doctors, IMO, however most of the stories under Moffat I thought were meh.
I think Tom Baker said the role is actor proof, I guess we will find out.