How about a crafting/gathering dungeon where you support an NPC battle by building catapults, bridges, crafting instance-lifespan gear. Also have NPC crafters and gatherers in mixed teams.

If you're a gatherer you can gather more materials for the crafters (NPC or your team players). If you're a crafter, you can use your skills to craft instance-lasting gear for the NPC combatants or gear for the gatherers so they can gather quicker and more.

NPC-gatherers can only gather at "safe" areas while player gatherers can gather wherever they can survive and potentially skip certain parts of a progression tree. NPC-crafters can only make NQ gear unless they have HQ materials. Player-crafters can making HQ gear with NQ materials.

Both player gatherers and player crafters give boosts to progress in their own way. The question becomes what do you give a boost on? Building up your production line or strengthening the NPC battle force? And when?