Did you have the same feeling than mine when Tonks has declared her love for Remus ? A not very credible couple right ? I was very disappointed when I read it. Remus is far too old for her. Now I have the explanation. It's a concerted marriage, no less, for stop the rumors about the lesbian Tonks and the gay Remus. You don't think so ? But JKR has especially created this couple in the purpose to stop all the Remus/Sirius stuff on the net. It's also for stop the Draco/Harry that she has hurried the relation between Harry and Ginny (maybe also why we see Draco with Pansy in the train).
So, ok, I can understand that she doesn't want to create a gay couple in her books (a simple romantic relationship of course, I don't mean any nc17 one, it's still a story for the youth), she has already enough to do with those crazy fundamentalists who accuse her to pervert kids and lead them to witchcraft and paganism. But why does she try to influence the fanfictions ? I don't think that she can stop people to write slash if they want. For me Tonks is still a lesbian.
And even if she has told that Viktor and Hermione relationship will not go further, even if she marry Hermione with Ron at the end of the 7th book, I can still make them divorce and marry Hermione with Krum ! Hehe !