I would love something along the difficulty of WoW Cataclism Heroic Dungeons. They were not overly hard but you could easily wipe if you failed the strat just once.
You actually needed to know the strat. Pull required CC, we dont have so a "good" fix could be to make Mass Pull a much harder thing to do. More priority target would be nice and removing ground mark could also greatly increase the difficulty.
But as people pointed, these dungeon are catch up. So all these change would probly fit a new difficulty mode better.