I do them as blood, but I can't see why a single melee isn't desirable for CMs at the moment. They all have little things that make them really good this time around, and aside from a couple bosses/trash packs, melee is really good in CMs. A lot of it has to do with our DPS tuning at the moment, and the heavy mobility of some of the boss encounters that hurt most range (not hunters).
Honestly when I step back I can see why nobody would want DKs in a pug group. A lot of pug groups just go slow with the goal of completing the dungeon for the daily, and for that purpose CC is actually quite good.
However if you want to get golds as a DPS DK you shouldn't have a problem. DKs are 100% viable for them and in quite few instances probably one of the better options for many of the CMs. There are some pretty stupid things you can dark simulacrum in the new instances which is a lot of the reasons DPS DKs would be sought after. Aside from that DK single target is still nice, our AoE is crazy, and mass grip/remorseless winter are really good for CMs that care about time (mass grip is probably the better option if you actually have a solid stun in your group already).
While I hear a lot of talk about RW, mass grip really is the shining talent for CMs. If you're going for optimal pulls and such, mass grip still acts as an interrupt (without DRing other stuns), and more importantly it performs something no other class can bring, that being a neat little pile. The side effect of the ability that is often overlooked is that it saves your group a massive amount of interrupts while you try to get ranged casters in close. For instance, we pull the entire room of the first boss in everbloom, I'd imagine that would be a nightmare without mass grip.
No idea if they are the most ideal for top of the line world first times, but they certainly aren't in the bottom tier as far as class selection goes.