Some ideas which I think are doable without suggesting complete new effects.

Soul Eater
I think rather than buffing soul eater it would be more effective to take soul eater out of grit and treat it more like siphon strike.
Grit: soul eater absorbs 100% of damage as HP
No Grit: Soul eater absorbs 50% of damage as HP

This alone could help ease the burden of healing a dark knight by a relatively small amount every 3 to 4 GCDs without needing to change the rest of our kit. It would function like a regen (weaker yes but still there) but on a 7 second tick rather than a 3 second tick. It would also make up for the missing passive mitigation of paladin and the higher uptime on mitigation of warrior while being different from both.

Delirium
I like the idea behind delirium, but I feel like either the cooldown needs to be reduced to 80 seconds, or it needs a stronger efffect. For example, since it is on a 2 minute cooldown why not make it double the duration of blood weapon/blood price rather than adding 8 or 16 seconds respectively. This would be a slight nerf to blood price, but would be a nice bump to blood weapon which I think most people would prefer to use it on.

Shadow Wall
This either needs a strong additional effect or a reduction in the cool down timer, ideally both. One cool effect, which would be worth the timer, would be to have a hit on shadow wall decrease the cost of the next skill by 20%. However, I think we are more likely to see a reduction in CD timer than a new effect.

The Blackest Night
Reduce the mp cost of this ability to 1800 mp. This solves the issues around no grit and TBN without buffing any potencies and brings the skill into line, cost wise, with grit.