I think Stephenie's reaction to the Midnight Sun leak is understandable. It was her baby, and someone went and ruined the fun of it all for her. If she doesn't ever finish it, yeah, it would suck, but I wouldn't blame her. I hope she does carry on writing Midnight Sun, even if it is just for herself, and not publishing it. I feel she should get the enjoyment of writing the story. Though, I would love for it to be completed. It would be great to have the whole collection.
I do like the idea of books by Stephenie about ghosts or mermaids. Especially ghosts; Stephenie doesn't do horror, as we all know, so it would be interesting to see what new mythology she would bring to the ghost story.