Well millions, and we've already been mixing for pretty much our entire history.
But I doubt we'll ever become a homogeneous people the world over (Though I bet that'd be a pretty baby), just reshuffle some genetic chairs and blur the edges on what we now think of as the races.
A lot of People will always think their culture and country is better than everyone else. In a certain way, it's good for competitions. Just don't be too patriotic and mock others for being different. Although, interracial relationships are still more acceptable than LGBT relationships. Also, besides amwf or bmwf, there are places in the world that rejects relationships because difference in social class or even different cities of the same country.