Nobody is really sure what will happen to ethnic groups, but my guess is that mixed races will grow and grow until every single soul is of the same color.Its a normal thing and will happen gradually. As far as I can tell, there are Asian people, Chinese,Caucasian, Hispanic people,  all over the world, mixing and mixing.It´s a sign that racism is ending , which is a good thing. In 2 thousand years or so, there will exist one colour, and racism will end, or so I hope. well, as other people may start saying, there will be no color, since there will only be one among humans.

the mixing may also happen because humans may start becoming less connected to the place they live than what they were 400000 years ago.

Hope this was what you were looking for!