I ask this all just because of curiosity, but I really hope it does not come across as racist as that is not my intent.
Are there any good black actors who would fit the role?
Isn't that a bit like asking "are there any good black actors"? There is absolutely nothing about the part that requires the "special talents" (whatever they may be) of Whitey to play it.
For that matter there's nothing about the part that requires a man to play it either.
I don't know any black UK actors, ok. I maybe know Elba, but other than that, I don't know of anyone else. As for the whole good part, I would hope they want someone good to play the role, but who knows. I certainly didn't know who Smith was before he landed the role of the Doctor so anyone can be a pleasant surprise.