REALLY random idea: A deep dungeon, but all Jobs have their PvP kits.

[Absimiliard]

This. If you give a PvP kit without the PvP mechanics (being usable by the mobs), too... that's most of the value left on the floor.

I mean, they used to make mobs that would stun, silence, sleep, or otherwise debuff the absolute crap out of you. I'm not sure why they stopped, but I'd love to see them brought back. Preferably more intelligently than in prior design, by which I mean the mobs utilizing their abilities at the best possible times to screw players over. A good example might be a boss or particularly powerful trash mob deciding to land a tankbuster then immediately stunning the healer so the tank is unable to be healed before the next auto - or interrupting, should the healer be hard casting a heal instead of using something instant. Could even start throwing in stuff like slowing or stunning random party members during major mechanics to leave them at risk of imminent unavoidable death (or at least a ton of damage) if the healer doesn't yoink them out of harm's way.

Of course, the above would have to be adjusted in the event someone went in alone. Otherwise they'd probably just get massacred outright.