I think it definitely helps if anything. at 20% leech, if they do 400k dps each. You could either pop it all for 400k hps or 20% of that always on.
Blood DK was already viable before, or at least it seems with 1 prot Paladin for extra spot heals.

I'd like more options in the mix and Blood DK's have a couple of utilities that are amazing for boxing such as grip