Here's an idea...
With the popularity of WarCraft III's hero units Blizzard decides to release a bastardized version of a Diablo 2 style hero game. "WarCraft III: Hero Legacy" where you pick between a Demon Hunter, Paladin, or various other hero units. The game will essentially be Diablo 2 in look and feel, but the story will follow the WarCraft III storyline.
The above seems unlikely (right?) so I'm hoping for SC2.