I doubt a Harry/Hermione scenario. I have heard that J.K. Rowling even considers that a brother/sister type of relationship.
I sort of got conned into watching some show the other night about the series, and she (Rowling) mentioned off-hand that it would awkward between the two H's. They had some third parties (one was a psychologist/whatever) there talking about it would be Ron/Hermione, because she was just like his mother, and the whole "men marry women who remind them of their mothers and women marry men who remind them of their fathers" thing. Felt like I was watching Oprah or Phil Donnahue or whatever.
I was a bit flabbergasted that people would be having such serious psychological discussions over young characters (especially when the last two or three books aren't even out yet). It is a sign though, that it'll have staying power since LOTR and other series have generated just as serious speculation/discussion.
It's went the opposite way of StarWars in regards to well-crafted characters, when it was revealed the whole brother/sister/father triangle in Empire/Jedi, there were all these discussions about the father/son thing. They go and do the sequels, and you end up with a whiny brat who deserved to be killed by his son.