Racial impurity is not a case in today's world to begin with. These fictional future Zendaya look alikes are what people sort out based on the question of "how a mixture of all people look on average?".
Here is the deal: It is impossible to mix all the people on the World. From 60.000 years now not everyone will have same racial ancestery to produce same medium brown skinned light brown eyed models they keep showing in these supposed science articles.
Lets assume every single nation and ethnic group are /pure/ now. We have to assume from now on each and every people will make the choice of reproducing to make all people of future to same genetical mixture. And all those mixtures will have same dominant/ressesive genes to show the same look. That one type model is just impossible.
You can see many siblings with very different physical attributes. I have a relative who have twin daughters; one of them is a green eyed blonde and the other is a dark brown eyed brunette. They have same ancestory from iron age to their own parents, hell they are they genetically closer to each other more than any person can be to them; yet a total stranger with no relation can share a physical attiribute with one of them other can not have.
For example, these beautiful ladies are twins:
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Racial mixture does not produce lookalikes today and it will not in future.
Other than the fact that it is pretty much impossible to see lookalikes with same skintones in distant future, that possibility is not worrisome or negative. It is not positive either; nationality, ethnicity, homelands are very much present in today's society despite racial mixture. I do not think our future milk coffee selves is a permenant solution.