Noah Berlatsky weighs in on the controversy over a black Hermione in the play "Harry Potter and the Cursed Child" here, for the Guardian. Says Mr. Berlatsky (in part):
If Hermione is black, then ... themes about racism become much more pointed. Hermione, remember, is the one person at Hogwarts who is horrified by the enslavement of the house elves. When she’s black, her sympathy inescapably becomes rooted in her racial identity – her knowledge of her own marginalised status, and of her own people’s history. Similarly, the racial epithets thrown her way by Draco Malfoy and others take on a greater weight and ugliness. When Malfoy calls her a “filthy little mudblood”, he’s referring to the fact that her parents are non-wizards, or muggles. But if Hermione is black, you have to read it also as a racial insult. If Hermione isn’t white, it can’t be coincidence that the “mud” in “mudblood” is brown.More about color-blind casting here and about casting Hermione as black here.