Black Guinevere did cause some snide remarks, but almost no noise even with the odd article stirring thing. (Especially since most of Merlin was all over the place anyway — along with ‘Robin: The Politically Correct Man’ as I heard the Robin Hood series of the time referred to, any ‘right on’ elements were overshadowed by other aspects) Sophie Okonedo didn’t get much noise (even though it was attempted to be stirred up) when she was Queen in the quasi-documentary, quasi Shakespeare ‘Broken Crown’ TV thing, largely because she’s considered an excellent actress, and because of that Shakespeare adaptation element.
The Snape thing I think is different, because the complexities of that character and his relationships would actively be harmed by inadvertently introducing an element of racism into things that casting a Black British actor would do. That’s my stance on it, tbh, and I think people that don’t see that either don’t know the character and stories, or the time and place they take place in. I can think of loads of *other* HP characters that could be cast with BAME actors (including Hermione, as has been done on stage — though with the mud blood thing from the books, and SPEW, it’s edge territory) and it not change the underlying meanings and relationships. But Snape would be unwise.
It is not really registering in the mainstream press to be honest, and I wouldn’t expect it to. There’s the same lack of mainstream noise about all the people sounding off that Heathcliff *should* be a black actor in Wuthering Heights (which shows that some people really read things, or pretend to have read them, with zero knowledge of the world when they were written, or indeed anything but the most modern literal understanding of words therein.)
As to the subject of the whole thread… well, I have just come to the conclusion that some people carry a bias without meaning to, and however well intentioned, shouldn’t be let near writing if there’s a risk of it showing. Gatwas problem isn’t that he was a ‘Black Doctor’ it was that he wasn’t decently written or costumed or shown as ‘The Doctor’ in Doctor Who. Maybe some of that was in his performance, but I suspect it’s higher up in the production chain. Just look at Mickey Smith as written in Rose et al. Production choices that were obviously red flags from before he was even on screen did for this incarnation.
Brits for the most part aren’t quite so race obsessed as to worry about it, and in general probably give even less of a monkeys about Doctor Who in general these days.