Doctor Strange scriptwriter C Robert Cargill appeared on YouTube podcast Double Toasted, talking about the casting of Tilda Swinton's casting as The Ancient One. And comparing it to the unwinnable Kobayashi Maru in the way people might react. Already there has been criticism for casting a white Scottish woman as a traditionally East Asian character.
Screen Rant has the transcription. Cargill says,
The Ancient One was a racist stereotype who comes from a region of the world that is in a very weird political place. He originates from Tibet, so if you acknowledge that Tibet is a place and that he's Tibetan, you risk alienating one billion people who think that that's bullshit and risk the Chinese government going, "Hey, you know one of the biggest film-watching countries in the world? We're not going to show your movie because you decided to get political." If we decide to go the other way and cater to China in particular and have him be in Tibet – if you think it's a good idea to cast a Chinese actress as a Tibetan character, you are out of your damn fool mind and have no idea what the f-ck you're talking about.
China is where much of the movie money is right now. But they did still cast a white actor instead of, say, an Indian actor, which would have been closer geographically and culturally.