Death Knight by now and know that it is going to be the game's first "hero" class -- unlocked by a level 80 quest and starting at a higher level than a non-hero character. But I'm not really wondering about Death Knights right now, but instead about other hero classes that might be in our future. It struck me as an odd move to release an expansion with a single hero class purely for practical reasons -- as soon as people start hitting level 80 with their mains, we're going to see a swarm of new baby Death Knight alts. (That Death Knight Spree isn't just a joke!) The best counter to this, in my opinion, would be more than one hero class in the expansion. Of course we'd still wind up with a lot of new hero class players, but at least there would be a variety of them. And on the forums Nethaera gives a bit of hope for future hero classes, though not in this expansion:
We are thinking at current that any future hero class additions will be made in expansions further along the line so that we can control just how many classes the game has and continue to work on attaining balance as we add them.
I'm still hoping they'll come around to the idea of more hero classes sooner, rather than later.