When I first read the books, well before the films, I visualised Hermione as mixed-race, because she was her very curly hair was mentioned. So Emma Watson was a very jarring casting for me. And I also assumed that Sirius and Lupin had a thing for each other (James had Lily, Sirius had Lupin, so Peter felt left out and rejected, hence he turned to the Dark Side). I found it a bit confusing when Lupin and Tonks got together. And I'm so boringly hetero-normative that I decided I must have been wrong, rather than realising that of course Lupin was actually bi.
So, in my opinion JK has the multi-ethnic and LGB stuff covered. After all, if it's not strictly relevant to the story, why mention it? Does she ever tell us where Cho comes from? Or Parvati? Not relevant. Use your imaginations.