One thing I do like about the DK's is that no target is going to get away from you, period. 4x Death Grip on a 15 second cooldown plus more Chains of Ice than you have cooldowns before they go immune.

I guess one would have to calculate if the DPS of 4x DK's is enough to overcome two healers output. I mean, if so... Yeah, it could work. You need two cooldowns to get your diseases up but after that you're going to be rocking them something fierce. Maybe if you prioritized their healers first so you could ensure keeping at least one locked down with Strangulate, BE silence, Ghoul Stun, etc etc.

The more I think about it, the more I think it could work. Hmmmm.