It is my considered opinion that casting actors according to their ethnicity is the worst part of Affirmative Action. Not casting the best actor for a role because he is not the right race is the definition of racism.
Disagree if you like, but it won't change my opinion.
I could be wrong, but I don't think Hollywood is subject to Affirmative Action, but it is subject to public opinion. If people are demanding more variety, or if the show is trying to appeal to a broad range of people, they will include different races and body types.
However, I do agree that you should also try to find the best actor available. Which is why I am really glad they cast Cumberbatch as Khan.