Ideally there should be enough available actors to authentically cast a film, and honest effort if there isn't. This makes me think of the 1961 "Flower Drum Song", about Chinese-Americans, written by a Chinese-American, yet a couple of leads are Japanese and Filipino (an honest attempt though). F.D.S. was later criticized for stereotyping, but also enjoyed a revival by Asian Americans (kind of laughing at the art form, perhaps in the way African Americans chose to laugh about Stepin' Fetchit, though F.D.S. seems much less gratuitous). I power-watched "Hawaii Five-O" recently, and though it sometimes had whites playing Asians (notably Anglo-Egyptian Khigh Dhiegh playing nefarious PRC's Wo Fat), they seemed authentic about 80% of the time (honest effort). It also makes me think of Mexican actors Anthony Quinn and Ricardo Montalban, who played everything from Chinese, Eskimos and Arabs to Greeks, Huns, and Native Americans. I suppose in a movie about Genghis Khan there may not be enough Mongolians to answer the casting call. Apparently Japanese actors sometimes play white people, a shortage of white actors there? Nice thing about America, the "rising tide" eventually gives everyone a chance, big opportunities for Ang Lee, Alice Wu, Lulu Wang, John M Chu, Justin Lin, etc.