There are many things Warcraft has going on, and we have made MANY enemies along the way. From factions such as the Burning Legion, to the Naga, there are many things Blizzard could do for the next expansion. However if you in control, who would you want to face? Would it be a straight enemy similar to BC, Wotlk, and Cata? Or a vague story such as classic, parts of cata? Or something even like MoP where it is about heroes..... kinda?
Edit: hopping* -_-