J.K. Rowling revealed she is not ruling out writing another book set in Harry Potter’s world.
Rowling would take another trip on the Hogwarts Express only if she had "a great idea," she said. "I don't want to go mechanically back in to that world and pick up loads of odds and ends and glue them together and go 'here we go.’ It would make a mockery of what those books mean to me."
But a new novel would center around characters other than The Boy who Lived. “Where Harry’s story is concerned, I’m done,’’ she said. Instead, she would craft a “sidestep’’ story, rather than a sequel or prequel. http://today.msnbc.msn.com/id/49177003/ns/today-books/#.UGXN7FHdeSA 
I think most of us would be thrilled with her writing a "sidestep" story... she could flesh out some of the other characters, go backward or forward in the history of Hogwarts or anything she felt like doing and I'd be happy! LOL
If you had your druthers, what characters would you like to see her include?