Random thoughts concerning drk skills since I'm bored at work on a night shift.
Delirium - For the next 15 seconds, any skill that uses blood refunds a portion of mana. Any skill that uses mana refunds a portion of blood. All blood/mana gains from combo skills are doubled.
The refund % from blood to mana and vice versa can be used as a tuning knob to control the damage output of the cooldown, same with the duration. The idea is to preserve some of the gameplay of the aoe style that drk had in SB, converting blood to mp and back again. You'd still keep using your main 123 combo to help fuel your meters, but would be using your BS/Edges at a very increased rate because each would help partially fill the other. At least this way you're still dealing with resource management, and you're not stuck spamming a single attack.

Living Shadow - The last 3 abilities used by the DRK (not including def% increases) will be copied by your shadow. 1 min cooldown, 50 blood. 3k mana. (maybe no mana)
The resource cost might be a little extensive, but having an ability that mimics your last three can bring a lot of decision making into the class, plus it feels like our final ability should eat up both of our resources. In an aoe pack? Save up some resource so you can flood twice and quietus, then pop the shadow to double up that aoe damage. Getting hit really hard? AD/SE/TBN and pop it for an extra burst of healing and shielding.
Might be a little bit too strong including TBN in it, but I like the idea of your shadow being able to come out and throw out attacks you want it to, according to the situation at hand, and it takes some forethought of which resources you wanna use/spend to really maximize it.