Currently damage is mostly dealt with by two types of players: tanks who mitigate it and healers who undo it. For tanks it's mostly about gear while for healers it's mostly about fast responses, anticipation of damage, and somehow surviving knowing that a single screw up can kill everyone. I admire healers for this. DPS don't do much in this process. You might see a ret throw up a sacred shield or maybe a mage or warlock throw up a specific absorb type, but in general DPS aren't involved in the damage control.
Let's change that.
I propose a way for DPS to increase their damage by protecting the raid. It would be a way to redirect certain types of hostile spells to themselves, absorbing most of the damage, and as they get more they accumulate spell combo points. These could be released for various devastating attacks.
Imagine you're on Thorim and Sif is throwing around a lot of frostbolts. You could throw up a resist aura and heal through them. Or, you could get a mage. They could redirect the bolts to themselves and with frost ward absorb the damage. After a while they could strike back with the absorbed damage. Other classes and specs would have similar abilities: shadow priests, warlocks, and DKs controlling shadow. Fire mages, destruction warlocks, and elemental shamans would control fire. Frost mages, DKs, and elemental shamans would control frost. Arcane mages, DKs, and warlocks would control arcane, though warlocks would retaliate with shadow damage. I spent too much time typing those out: the idea isn't meant to be so specific.
Lore-wise some of these might not make enough sense. A warlock protecting the group doesn't seem to fit, but maybe if it's boosting his ability to hurt other people? If it's a net gain in pain, a pain profit if you will, perhaps he'd do it. Other classes would seem to make more sense since several are healers or tanks and mages aren't social rejects (well, maybe only in lore)*. Hunters might have some sort of special arrow which they shoot at spells to catch them and then can be shot back, maybe this would tie into arcane shot.
What would rogues do that would help the group? They're not nice or even casters, so I'm not seeing any potential spell-control utility. Maybe they could have an anti-melee ability: looping a string around the enemy's weapon and pulling it taut, so when they swing at the tank it gets pulled back towards them.
* No crying, it's a joke, I have enough water for now.