I've actually thought about this as well. I love running healers in traditional mmos, and was hoping for something like this in destiny. My idea was an arc subclass for the warlock, with a grenade option that buffs allies Shields, like a thrown overshield generator. Warlock melee would create a health and shield buff wave upon a kill, boosting max health and Shields in the radius for several seconds. The super would be similar to the titan bubble, except it's not a bubble, but a section of lightning on the ground, healing all players inside it and causing arc damage to enemies. And you can shoot from out of it. Obviously, it wouldn't last as long as a bubble.