Yeah...you could use your blood to heal, and put life leeching skills in the same tree, which would work in tandem.

Something like:

Leech: cost 16 blood - does 35-65 damage. Heals self for 100-150. Charged version is an aoe. 10 second cool down

Blood transfusion: cost 16 blood - heals up to 2 allies in a 12 meter range for 150-200 blood. Charged version heals 4 allies and increase their armor by +2. 3 second cool down.

Ancient blood: cost 30 blood - regenerates 50 blood per second, increases armor +25, and grants immunity from immobilizing effects for 15 seconds. Charge version last for 25. Ancient blood also increases the damage of other spell in the healing tree by +5. 60 second cold down.

Bloodletter: cost 30 blood - aoe damage over time spell that does 40 damage per second for 5 seconds, and heals party members within 12 meters of victims for 80 health per second for 5 seconds. Charged version increases armor by +15 and effect to 7 seconds. cool down 10 seconds.

Basically, the healing tree would be a low damage, healing, and pvp tanking tree (because all healers in pvp pretty much tank). The person can heal their party members, or tank with leech spells...but not at the same time. Also, it isn't a dps tree, more like a survivability tree with healing utility, which would take forever to kill things, so it isn't crazy op. All the spells could be based on attack and damage, but just applied to healing and damage.

Healer synergy is one of the best aspects to playing an mmo, over a one player game. I definitely hope that STS considering one. I think it would be a great thing.