Setting-wise, I really would've liked to see "hard" versions of some of the SB dungeons like Bardam's Mettle (Perhaps we could delve deeper into the ruins that comprise the latter third of the dungeon).

As far as the dungeon mechanics go, I like interesting trash mobs that do things other then just the basic telegraphed AoEs, especially the miniboss sort like the ghost at the end of Sirensong Sea. Environmental hazards that threaten the player and/or can be used against the enemies also spice things up a bit.