Here's what will happen. They will drop the expansion names entirely and call it simply 'Warcraft'; it will be an ongoing service that gets only patches and not expansions; it will satisfy both those that want a simpler game and those that want WoW 2 and it will make the game looks less daunting to those that never tried it before (they're scared if they see 99 expansions).
As for expansion theme; murlocs; the littlest person can change the course of the future.