This is sincerely my dream. I loved making dungeons/gauntlets/mazes in minecraft and made several mods for oblivion back in the day with cool dungeons. Would love nothing more
Like housing. You design a layout using a simple tool, skin it using a theme such as a castle or cave, then you populate it with enemies and bosses that you train to become tougher. Players get rewards in the form of coffers.
Players would just make them super easy and farm them solo for coffers. Imagine if parsing on training dummies gave you rewards.
These kinds of sandboxes are fine for solo games. But In multiplayer games with lots of competition, both direct (PvP) and via PvE leaderboards, you don't want to give players too much of a rewarding sandbox. In a game that is seriously dependent on "network effects", you also don't want to give players too much reason to abandon the game world and stay in their own little private dungeons all day.
Maybe if they were like training dummies, with absolutely zero rewards, and just for practice?
One thing I would like to see in a somewhat similar vein is to provide a dungeon creation tool, players can submit dungeon designs to PTS, other players can peer review and critique. Finally, the best rated player PTS dungeons get sent to ZOS for final review, and then released as live game content.
So, a way to get more dungeon content added to game, and likely some very creative dungeons, but only the most balanced and well-designed dungeons. And specifically designed for the entire player base, not just self-indulgent individual content with rewards.