Didn't the cast for the play(the one with Harry Potter kids) also race swap Hermione?
Honestly it wouldn't surprise me.
That stuff doesn't really bother me, plays have a fairly limited audience and could even be run in multiple places with very different casts. It would be an issue if suddenly Hermione is now ALWAYS played by a black actress no matter what. Plays, to me, have the max amount of actor leeway because they have to be put up by whoever is there. So a school doing this play would just cast the students, so makes sense that the ethnicities of the actors would directly reflect the composition of the current theater class.
But a TV show, with a GLOBAL market, has to think a lot harder about what the audience really wants (versus what the creators want to serve up). HP, to me, is selling a kind of mythic tale of England and relies heavily on a Victorian aesthetic, which includes casting almost all white folk because that's just what lives in almost all of england. And IF there were other ethnicities, most of them should be southern asian, not black. Trying to "Cast the world" into harry potter, but not significantly changing the story to accommodate it, won't feel right to most everyone. And if they do make Hogwarts a global school, instead of a regional one, then I think the "britishness" that so characterizes the story will also be lost.
They really can't "have their [casting] cake and eat it [retain the flavor of the books and visuals of the films]". This isn't a Bridgerton situation, though I suspect they will go that route. They should heed the lessons of Rings of Power (and to a lesser extent Wheel of Time) and realize that book lore and especially a previous establishing film series can REALLY focus the audience and if you just assume they will still show up that can be a VERY expensive mistake.
Now a lot of current stuff is being deliberately written to avoid any and all defining physical characteristics like skin, eye, and hair color so it can be color wheel cast for the inevitable adaptation. But Harry Potter, through the authors own art, has a specific casting particular to the place it is representing.
Ultimately I don't think casting "for color" will make or break this show. But I don't think they are being genuine with "open casting" either. Just admit to a quota system, own it, and then let the actors win us over instead of the gaslighting we are being fed instead.