My gut reaction is opposed to both changes, particularly the "white". But I'm not sure I've a rational basis for my objection. Our designations for other racial groupings are capitalized: Asian-Americans, Latino/Hispanic Americans, African Americans; Pacific Islander Americans, Native Americans. To be consistent in my opposition don't I have to come up with substitutes for those groupings.
I'm not sure, top of my head, of the difference between African-American and black--I know there's a perceived problem in distinguishing between immigrant African-Americans and antebellum African-Americans but does the black/African-American terminology handle that distinction? (Personally I think the perceived differential might point to an important dimension in American culture, but that's an issue for another post.)
I guess my reaction, as shown in a tweet this morning, is concern over reifying differences. To me "black versus white" is different than "White versus Black". A George Floyd demonstration which includes "Blacks" and "Whites" feels different than a "black and white" demonstration (though I suppose a careful writer might say "biracial protesters" or something similar, which leads to the possibly that forcing writers to capitalize "Whites" will drive some to avoid the racial designation entirely.
Another part of my reaction might be discomfort at being forced to consider myself as part of a racial group, rather than assume membership in the majority culture (at least as U.S. is currently constituted).