Something I would love, if you're taking suggestions, is a rune/accessory that stops you from gaining EXP, because sometimes I just want to grind for money and stuff without worrying about over-leveling.
Nightmare mode Labyrinth is the main issue here and perhaps needs some rebalancing. Its a fun idea to keep fights challenging and leveling without just grinding static enemies in large numbers but it also rather quickly escalates your strength to the point where almost anything outside of it becomes utterly trivial.