Something that MIGHT keep Lv. 50+ dungeons from being too easy...
I heavily emphasize the word "might" because I'm not sure it's been done in MMOs before.
Some of us have offered that SE should cap our item levels in certain dungeons past 50. While it sounds reasonable, I highly doubt it would be workable in a practical situation. On top of this, it really doesn't allow us to put our gear to full use.
My suggestion would be to allow enemies to adjust their levels to match our average item levels--something similar to FFVIII's system that prevented us from outleveling everything. If SE did this right, and that's something we can't always take as a given, it certainly could give people the challenge they desire and force more deliberate gameplay throughout a dungeon.