Phew....! Such a profound lack of understanding.
The point of this essay...this "simplistic" essay...is not really that "America is running out of white people," but that "whiteness" is on the run. White supremacy/white racism are being challenged in ways that are different (and more effective) than ever before.
I know you won't like this but it's just a fact. Every single so-called white person born and reared in this country is a white supremacist/white racist, whether they know it or not, whether they accept it or not. All white people benefit from this system of privileging whiteness -- again whether you know it or not. Whether you accept it or not.
"If you don't understand white supremacy, everything else will only confuse you" -- Neely Fuller.