The Current Hero classes, Death Knight and Demon Hunter are REALLY cool. I like how Death Knight tried to add a really unique resource system, and Demon Hunter tries to do things that no other class can. But in the long run, they are built and balanced like any of the other core classes.
I would really like to see some “Hero” Classes that shake things up as far as play style. There are few ‘challenge mode’ things that people already do in wow that could lend themselves to this.
For example, some people play a Pacifist. They don’t do quests or kill mobs, the level up through professions and other none-aggressive means. That would be a real game changing class. At level ten you could pick between an Artisan, or a Diplomat for your specialization. Artisan could increase your efficiency with your professions, possibly opening up extra slots. and Diplomat could give you bonuses to reputations, let you learn other languages, and possibly make you neutral to the opposing faction. ((this class would not be able to swap specs after they had been chosen))
Something similar could be done for the Ironman challenge, but that might work more as a template of restrictions for the current classes, rather than a whole new class.