the question asked by the OP was what would the next hero class be, not if there was going to be a hero class.
And cata is the emerald dream expansion, and i did watch blizzcon. Cata has Furion, the dragonflights, the old gods, its pretty clear the nightmare will be dealt with in Cata. If there was an emerald dream expansion, what would it be about? Obviously exploring a hazy green copy of azeroth wouldn't be that interesting, and if the dragonflights and the old gods are dealt with in cata, what kind of conflict would occur? I would attain a basic knowledge of the expansion that is gonna be out in a month before I decide to troll.