I would like to see a choice of standard, expert, or masters level difficulties for all of the dungeons (or solo, normal, and hard modes)
For example:
--Cathedral of Flames as it now stands = Standard
--Cathedral of Flames in Hard Mode = Expert
--Cathedral of Flames (an even harder version or perhaps a timed version) could be added for Masters
--Rhaegar's Menagerie made shorter (i.e., by removing some mobs) and/or a bit easier could be added for Standard
--Rhaegar's Menagerie as it stands = Expert
--Rhaegar's in Hard Mode = Masters
Basically, I'd like to see easier/quicker versions of the harder/longer dungeons (e.g., Rhaegar's or Frostmaw) and harder versions of the dungeons that are "quick and easy" (or so I hear on the forums

This would just provide players with more options in how they want to play and what dungeons they can enter.