A never ending dungeon that scales difficulty with each floor.
How would the community feel about an instanced dungeon that progressively got more difficult with each floor traveled?
Let's say the dungeon starts you at Lv50 mobs (these could either be created by random or be per-determined NM/boss mob with a few weaker ones), and to progress deeper into the dungeon you must kill all of the mobs, maybe within a certain time limit? With each floor, the mobs will scale and become stronger. Ideally, this dungeon could have no bottom floor, or perhaps a floor ending with Lv99 mobs. There could be nice drops/gear for finishing different more floors, but it could be a competition for free-companies to try to progress further down.