I wouldn't mind some backstory kind of stuff (the founding of the school, the stories of the professors, parents, Voldemort, etc.., maybe some of the stories of the various ghosts (their time in school and until they died, how they died, their time as ghosts in the school, etc..), and so on..). I'm kind of torn on a continuation and think it could either be a smashing success or total flop, depending on how it's done/what sort of antagonist/plot twist is put in, but I'd almost rather it just be left as is because if it is a flop, it'll put a sour taste on the whole series, at least for me.