In my opinion, BC is a 'side story' and going to another planet so early in the life of an MMO was probably a mistake (don't get me wrong I love BC)...
What if Blizzard changed it up a bit. What if after Classic; they move straight to Wrath? BUT... Instead of grinding it out to 70 or 80 they introduce some other type of time constraint and leave us at 60... And never introduce flying mounts; or dungeon finder... Obviously a few aspects would have to be changed, places that require flying, etc.
So Wrath would just end up being a really long extension of Classic, basically.
I know demons are central to the Warcraft story, but to me it just feels like Blizzard went about it all wrong.