I am totally in for this in leveling dungeons, it would mean instaqueues, and it would mean NO questing at all for leveling.
Even better put a random component on it for the classes than can do more than one rol, so if i enter with my druids, i can be assigned DPS, healer or tank, it would add more variety to the dungeoning, and it would take me out of my comfort zone (DPS), it will make some of that content quite challenging, as i have never tanked or healed in this game.