The healer discussion is an interesting one. Here are my thoughts. If I ever wanted to run this comp, I'd have all healer types available, so I hope I'm not too biased for or against any class.

Priest: Probably not as durable as the rest. Good AoE healing tools, which is probably still important. AoE fear is pretty decent, and I think you've overlooked that.

Pally: The bubble advantage is huge, provided you take care of the classes that can bust it. I think the thing that's nice about it is you can buy a lot of time with the bubble. Good players will switch off of your healer when they see this, and they're probably not going to pick the same DK to focus during the duration. Buff is good, healing pretty good, survivability is probably most important. Pally-centered AoE heal will be interesting, should you choose to intermingle with your team.

Druid: I agree with your points. I think you overlook the ability to use stealth, however. I'd keep my druid healer stealthed at all times and pop him out only as needed. Thorns might have some utility, too.

Shaman: Tremor would be a huge help, despite your other defenses. Bloodlust is also nice... Chain heal is made for this group, and earth shield on yourself plus good healing tools (and mail/shield) will make you somewhat robust.

Overall, you make some great points for the comp... I have two main overriding concerns:

* The power of the comp centers on a new re-work of a class and a few key abilities (esp. howling blast). Blizzard could retool frost DK in several minor ways that neuters the effectiveness of the team. Contrast this with Elemental Shamans, where the changes were incremental, pretty balanced, and we've seen almost no tweaking of the comp for many, many PTR patches. Knowing my luck, I'd roll up some DKs to pair with my pally and get them to 85 just in time to have major changes go through...

* The team comp really shines with 5 people. I agree it would be better to have another player as the healer-- even so, you're taking up 5 slots of a 10v10 BG. Somewhere, your team is defending a node with 2 people instead of 3 as a result. This is a non-issue for Arena, admittedly. For competitive BG, this pretty much guarantees you take up 5 slots to support the 4 DPS. (Contrast that with Shaman, who can quadbox effectively with some decent survivability built-in.)

All that said, I have healers available and getting DKs leveled up is inherently easier than any other new team... It's tempting.

I think I'll let you (and others) show us how awesome it can be at 85 before I take the plunge!