What would be cool is an exotic that adds a unique hazard to a rift based on subclass choice. Wouldn't be too hard either since Stasis is already getting something similar. Solar subclass rifts ignite enemies that enter it for a steady DoT, void could draw enemies in and/or disrupt ability use, arc could repel enemies with bolts of energy (ie riskier rift rushing / deterrence for players and mobs). That or maybe an instant AoE pulse heal that trades the overshield a healing rift rift can potentially (eventually) give for an instant burst of full health to friendlies near the warlock. Empowering rift maybe gives a short duration buff that makes all hits crits that lasts half the duration of a normal empowering rift. Stuff like that. You know, give rifts some teeth to them or some mobility benefits that they sorely lack in this mobility-heavy sandbox.