Blizz can't balance it. They're trying to be heroes, and try to make some new shinies for people in the form of giving a class a new role, and they're going to screw with the entire spec. Look at it now in beta. They think they can take a damage dealing spec, slap a glyph on it to reduce the damage you take and give you a taunt, and not expect it to be OP. This is going to be the bane of warlocks for a long time. It's going to create some serious drama. Demo locks are walking walking level 90 Illidans on beta atm.
Look at this shit. A shaman opening up on a demo lock. It's hilarious.
http://youtu.be/juidpkdexGY