They’re already doing it in a lot of movies. In comic book movies, Nick Fury, Kingpin and Deadshot were white characters cast with black actors. The upcoming Flash movie casts Flash’s white girlfriend with a black actress. And it’s rumored that in the upcoming Spider-Man movie, Mary Jane will be played by a black or “mixed” actress.
Seems to be unheard of to find the opposite happening though, where a white actor plays a black or brown role.
However, we do see that with some Asian roles. In Dr. Strange, the Ancient One was an Asian male in the comic books, which the movie changed to a white woman. The upcoming Ghost in the Shell casts Scarlet Johannsen as an Asian character. The yellows don’t get quite as much coddling from liberals as the browns and blacks. Of course affirmative action already devastates the college admissions opportunities of hardworking Asian kids nationwide.
The Ancient One was Tibetan in the comics, but Marvel Movies can’t afford to piss of China. So we get a British woman instead.