It's been mentioned in another thread that we could use Darkside as a resource, yeah. I personally am fond of the idea of giving something akin to Death Strike on World of Warcraft for us to spend Darkside on. (instead of pooled damage we've taken, though, the damage dealt and potency of healing would depend on the amount of Darkside consumed to use it). That would give us some form of sustain on demand if we make it its own standalone GCD.