It would work kinda like a normal dungeon except 1 DPS would be replaced by whatever crafting job the dungeon requires.... the way the dungeon would work is that certain items that are exclusive to that dungeon would either be dropped by enemies killed or picked up along the way in which crafters would have to craft into a key or item that opens a door that allows to group to proceed further into the dungeons, and boss fights might have a similar function where the boss or adds drop stuff constantly throughout the fight and the crafter would have to use said items and keep the CPS (yes I just made that up lol Crafts per second) coming that would slow down the adds swarming the party or stop the boss from unleashing is ultimate party wiping attack.
Just something that keeps crafters and gatherers more involved... I hear 1.0 had something like that in Hamlets where they were needed to make stuff during the battle that the healers, tanks and DPS needed to win or what not. That sounds fun. Im also not a HUGE fan of having control over Hqing that makes HQ too easy and thus not as rare and expensive as lets say XI's crafting was, plus with XIs crafting you didnt need recipes you just needed the right level and items so crafting was a mystery as you had no ides what you could craft (unless you looked online or used a guide) until you threw random items together and see what happened. I kinda liked that.