I think something like this would be nice if they worked it into the expert roulette. The level 50, 60 and 70 dungeons are already tuned to have the right amount of mechanics for an "expert" dungeon, so they just need to have their hp and damage values bumped up to the appropriate level. What I'm thinking is to have the 2 dungeons (or whatever) that are most recent plus one older dungeon that changes on a weekly basis to add a bit of variety to expert roulette. The rewards would be the matching rewards for the current expert roulette.

Leveling dungeons are fine imo and there is plenty of chance to re-play them while leveling other classes.

As far as the potential for more difficult dungeons, I'm not in favour of just pushing the numbers up on existing dungeons. I'm also don't want to see random mechanics or chance determining the difficulty; we already have deep dungeon and that is what it is. The thing that makes this games dungeons so good is that they are designed as a whole with planned out encounters and mechanics. I'd much rather see new dungeons (or things like the Hard versions of dungeons where they are re-made into new dungeons) that are designed as a whole with the higher difficulty in mind.