It'd be neat if a dungeon maker could be added.
Firstly, no loot except coin/gems and xp, all auto-generated based on the monsters and at less value than similar official quests, to prevent them from being farms yet also not being entirely worthless. Alternatively, make loot amount come with requirements preventing overly easy wins.
Okay, on to the meat of the idea.
Narratively in the game, these are just illusions telling a story, similar to that gnome Illusionist quest.
No need for this to be complicated, just provide some map tiles that fit together on a grid that automatically place walls on any openings leading to blank space. You can break these into tilesets if that is required for memory management.
A player can create one by going into a special room that has these tiles as items in a chest, and a grid on the ground at 1/4 to 1/6 scale, allowing the player to walk around placing the "items" onto the grid. Then they can go onto the mapm with it being loaded up based on the tile items they placed, and inside they get props, npc and monster tokens, trap/trigger tokens, etc. They can walk around the quest, -grant a quest item that generates a dimension door spell so they can have one-way sections) and they place these tokens and triggers. A trigger can have different types, for example, a trigger ambush item can be placed once, then some monster tokens placed in hidden holes, then the trigger item is used and all the monster tokens placed between the trigger being placed and subsequently used would then be set to spawn and attack when players reach the trigger. Similarly, this can be done for many things to create an adventure.
The difficult but important part, npcs and stories. There are story items that simply display text already in game, you can allow these to be placed and allow text to be entered.
Additionally, combine that with a set of triggers with allow text entry, allows you to have npcs de/spawn, move, act, and speak.
Conversations with choices would be a bit more difficult to do, but can still be done by nesting triggers.