NOTE: This is not an idea for a future expansion, but rather a patch that would be awesome to do in Cataclysm.
When Deathwing returned to Azeroth, the whole world was reforged in molten flame. And Northrend was affected as well. The Destroyer appeared in Northrend's frozen skies and reshaped the land as well. Now his agents zealously patrol the land, seeking to fulfill their master's vision of death and destruction.