A couple of thousand years of uninterrupted progress...
might result in a homogenized human race. Once upon a time I thought that would be a great thing. I still think it would not be a bad thing, but it it probably unimportant.
Uninterrupted progress for that long would probably mean we had solved most of our social problems. My fears are more for fundamentalist religion vs racial problems. I have seen great progress in racial matters in my lifetime, while religious fundamentalism is almost viral.
As far as skin color goes, I have seen predictions that color will be optional long before racial mixing gets anywhere.