This feature would be GREAT for map making, tho I expect it to be quite difficult

I did manage to create a KubeJS Script that allow custom loot but if it was built in, it would be MUCH better

Chests usually roll their loot when the player opens the chest. I guess it could roll the loot when the player approaches near by?

But, this mod needs to have the items displayed visibly. Also it relies on client side heuristics to determine how to display items, which it could request the approaching player for how an item should be displayed. Maybe we should just change the heuristic to work on the server side...