Well, it’s similar to “Asian” and “black” in that respect - they are American categories created by a nation where the variety of migrations reduced each group to their barest, most obvious similarities.
(And of course, going by migrations, the various whites are different groups, thus tumblr resident elementarynationalism trying to get the Poles counted as white by the other racial nationalists bumps into the legacy the legacy of the Third Reich and other stuff. Which is kind of amusing to watch, since the infighting prevents them from actually
getting
any kind of coherent power to make Britain white.)
And one could do a “White Festival” in the same sense one did an “Asian Festival”, and have a Polish booth, an Italian booth, a booth with terrible British food, etc. But in America, people aren’t quite “from” those cultures anymore, and after enough generations they aren’t really “from” Japanese culture either, which is how a unified “Asian” identity is even possible given historical attitudes in the region.
(And for a friend or two of mine, it isn’t clear just what booth they’d be at at the “Asian Festival”.)
There are still some rates of difference and ethnicity, but it’d be a bit strange. Birdwatching, apparently, is a thing we’d need for our Not-Numbingly-Racist Post-European Cultural Whiteness Festival. And even then, it isn’t purely a white activity, just one which is apparently lopsidedly white.
But on the other hand, I don’t think the “end whiteness” people are actually… I don’t think they actually want to dissolve whiteness back into its constituent parts or into nothing, and they don’t want to dissolve blackness or Asianess, either.
From what I can see, they still believe in intergenerational ethnic collective justice. Trying to end a unified American white identity necessarily requires discarding the idea of intergenerational ethnic collective justice, and if you believe that individuals now owe payment for ancestors past as a group, then you still very much believe in whiteness, just in a negative form.