... What would it be? As it is, warlocks already have a variety of demons for seemingly every occasion, yet in my mind's eye, I imagine warlocks being able to summon a much greater number than just 4 (or 5, depending on your talents). I close my eyes and envision a mad little gnome cackling as 5 or 10 minor demons come popping out of a portal he has just opened up. In fact, a demonology warlock in particular should be able to do everything he or she needed with the assistance of demons, is it not? It's true the Felguard is a nice pet -- but is he that nice?
So just for fun, let's play "imaginary abilities": what would you envision for walocks' evil little minions in the next expansion?