Maggie Q is one of the biggest action stars on Earth right now, though she's better known in Hong Kong than the US. And her profile in the US has been on the rise. It makes perfect sense that they'd want to cast the best, and not rule her out for trivial reasons like ethnicity. After all, it's not like there's anything about the character that requires her to be a given race. And it's not like she hasn't changed nationality before, from French to American (and possibly to Canadian?). Or in terms of actresses, from French to American to Australian, and now to a Vietnamese-American actress born in Hawaii.