Eh, healing your party is something blood has flirted with several times. (SL blood tap conduit). AMZ is a strong damage reduction CD. Group wide leech. It’s not a stretch by any means. I don’t think it fits unholy though.
Ideas I’ve seen posted before:
You could make blood a dedicated tank healer subspec if you wanted to. Treat it like beacon, have them link to a health pool and use a melee/death strike rotation to heal the damage back. This couldnt reduce tank damage taken because that would throw raid balance out the window, just probably copy some portion to the DK who would then replicate healing done with who they link with. You could also provide some shields through the mastery.
Blood worms could provide rot damage heals to the raid, and make them more potent for 5 man content.
Blood boil or the disease can also give you some aoe proc to heal your team for a small amount.
Blood could grant more group wide leech for burst windows.
Can lean into the bone shield fantasy and allow you to cast it on others for various benefits. If bone shield is applied to someone you can death coil to heal all targets with your bone shield applied.
Give another spec a spirit link CD since it fits the fantasy of the spec.
Heart strike or marrowrend putting a debuff on the target that gives attackers leech or a chance to heal.
This way DS becomes your big heal, death coil becomes your medium or spread heal, you toss around some shields, and blood worms/disease/debuff handle rot damage.
Remember when lich born would radiate death coils? There’s an aoe heal CD right there if you keep the death coil as a ranged heal idea. Consumption can be another big aoe heal/shield for raids. AMZ is your big damage reduction tool. That’s 3 solid cooldowns right there.
Lots you can do here. The tools are all there. It would very much so fit the theme of a lot of the kit without breaking class resonance. Not hard to picture a unit of the ebon blade having 1-2 medic style dks hurling death coils around making sure the front line guys are tip top shape for the fight…