Looking at the 7.2 PTR Blood Dks might have something going for them. While it's not 100% PTR, things can still change i've been watching the Vampiric Aura Artifact Trait evolve over time.

Each time you use Consumption (45sec CD) you and 4 allies gain 20% Leech for 15 seconds. Depending on how it interacts that's 100% leech 1/3rd of the time or staggered a constant 20% leech buff. Not to mention the 25% additional leech you gain when blood shield is up due to another trait. If all is right that's a possible 125% leech if it all stacks additive.

Then there is the other new trait. Souldrinker
Overhealing done by Death Strike and Consumption increases your maximum health by 50% of the overheal amount, stacking up to a maximum of 30% of your health.
With so much leech staying at max health would be rather easy, so I'd imagine this trait would cap out.

What do you guys think?