I don't buy it. Adult literature might do that for the heroic tragedy component, and while the Harry Potter books appeal strongly to adults, it's still children's literature at heart and the readership base remains primarily children.

It would be a brave turn for the books to take -- might even be the best choice artistically -- but I completely disbelieve that she would do something like that to the kids who literally grew up reading these books.

She's clearly setting up Harry as the Defense Against the Dark Arts professor: look at some of the comments about it in book #5 ("You're the best Defense Against the Dark Arts instructor we've ever had!")