Instanced Non-Objective Dungeons

[Ehayte]

With regards to the changing class thing, maybe make it so there are designated 'safe-spots' placed sparingly throughout the map? Think like the one in frontlines, but just in more places. They should require no aggro on mobs to enter and allow you to change classes and whatever there.

My original idea and in the OP I would say at any point you aren't in combat. Each chamber in which you fought something would lock like a boss battle, so you can only change classes pre-combat and post-combat

Perhaps randomised debuffs then? nothing too drastic of course. But if the dungeon goes until you die, it may be worth giving a helping hand in the matter. Say like a -5% party-wide HP debuff or a 3 yalm range debuff on ranged classes. Maybe turning one DPS into a frog for 10 seconds mid-battle?

For sure - that's kind of the idea behind the randomly triggered events (causing AE dmg, red zones, etc). I think everything should be temporary though (15-30 seconds), if you remember FFVII's battle arena it could sometimes become impossible to win if you got the wrong combination of debuffs. I think it accomplishes its goal of being real, meaty content only by keeping the integrity of playing your class normally in-tact.