What if they did a map style dungeon.. think Aurum Veil opening area+ branching paths from Thousand Maws an maybe a touch of Eureka where the bosses spawn in to open areas you cleared out once their minions were gone..

So you get a dungeon with many open areas an lots of mobs you can pull as many or as few as comfortable.. then once that area is cleared boss spawns in the same area.. no stop between the final add an boss.. so you wanna work with your party to keep HP/MP and cooldowns ready for the boss.

Once you've completed an open zone its branching paths to the next area.. different mobs and mini bosses spawns depending which pathway you take.. all leading into the second an final boss for the dungeon..

Ofcourse chests down each branching path and chance to get all of them if you backtrack.. maybe add in special random chance mobs that drops chests like from the canals?