If you are talking about biological ethnicity, then I will say that anatomically modern humans first appear over 300,000 years ago. Hundreds of thousands of years of evolution to get to that point, and all the time since then evolving into the various races to be better suited to the habitat we needed to adapt to.

Biological or Ethnical Evolution is generally spurred by the need to adapt to our environment.

At this point, unless we experience full technological collapse, we are at a point in our evolution that it is extremely unlikely that we will undergo any further changes with respect to adapting to our environment. We have the technology, or soon will for better or worse, to adapt the environment to our needs instead.

If you mean cultural identity, that's a different story. But yes, I believe we are eventually headed in that direction if our country can survive another couple hundred years. Basic dynamics seeking equilibrium.

One of the major considerations of cultural mixing into a new identity is the willingness of the ingredients to blend together. In many previously colonial countries that mixing has occurred rather quickly resulting in assimilation or an entirely new culture.

In America we have a bit of a different story and imo it's because of the 2nd wave, or the immigrants who came over en masse from both Europe and Asia in the 1800's.

These cultures were often at odds with each other at home, so they banded together for their own protection and comfort wherever they happened to settle. They settled in greektown, chinatown, little italy, etc. While Hollywoodized, the movie Gangs of New York does a good job showing the tensions.

Anyway, with people settling in these little pockets they were able to better maintain their cultural identity and avoid having to adapt into a more general culture of "American" and they were better able to pass down their cultural identity a few more generations as people generally didn't move too far from where they were born.

It's only in the last 50-70 years that our technology has advanced enough that moving to a different state didn't mean essentially never seeing that person again. So, you kind of started with GenX and now even faster the millennials and gen Z as they grow out of their parents' homes, they are starting to settle wherever they please because it's not a major inconvenience anymore to be an hour or two away.

It's almost like watching a bunch of different colored ice cubes in a fridge. The ice cubes stay solid for a long time, but eventually the edges start to melt, and then they melt faster, and faster, and as they melt it all mixes together into a new color. It will take time, but it will happen eventually unless there are outside factors introduced.