With ethnic intermarriage growing ever more common, the entire matter of ethnic distribution is a sideshow. It's only worth noting to the extent that anti-Caucasian bias reveals the racism of the Left.
My daughter is half Philippino, and has simply been raised to be an American.
Also, your view of ethnic trends of the next 125-200 years is based on the previous paradigm that has endured throughout human history to this day. Two things are permanently changing that paradigm. The first is increased mobility of human populations, worldwide. But that simply accelerates an ongoing trend.
The second is a technological development that is going to change all of our perspectives on ethnicity within two or three generations: gene-splicing and the inclusion of the DNA of animals into the human genome. Our grandchildren and great grandchildren will face the dilemma of how to co-exist on with these new... humans(?).
If folks feel comfortable with a hidden dog gene here or frog gene there, how about a person with genetically engineered cat-eyes, with vertical pupils and third eyelids? The technology to make that happen will be available in a decade or two.
The lesson of WMD proliferation is that technological genies excape from the lamps, and will be aquired by unthinking and unethical people.
Forget about ethnicity, that's not the issue. It diverts our energies and provides ammunition for demagoguery to our opponents. The issues are assimilation to our language and culture (inseperable), and the erosion of American sovereignty and rule of law with respect to Illegal Aliens.
With this being said, I do think that it is a priority to solidify relationships with already existing minorities in the country. Thus, we don't need to admit more individuals and create ever more voters for the Democratic machine, as well as more followers of the socialists. We also don't need more people talking about how they're going to vote against the "white man" and his party.
I've stated previously that I believe that relationships between whites and blacks are getting better. Thus, why would you want to import more individuals who will defeat the purpose.
As far as the animal gene stuff goes, I don't think that it will take on. To me, you'd be considered a freak. Furthermore, I don't know if its possible because you're dealing with totally different species.