I can think of many useful applications for a system of temporary items, or items that change/disappear after a certain number of turns. I don't know how other roguelikes deal with this, but in Dredmor I'd like to see it work the follow way. On floor 1 a Fresh steak is spawned, in 300 turns, it will become raw steak, in 300 more, it becomes aged steak. I'd also like to see items like this: A spell effect spawns the item "Burning-Fuse dynamite" in 5 turns, the item is deleted and the spell effect "Dynamite explosion" is cast. It would also make possible items like "Cursed blinking blade", every 15 turns, the target (carrier of the blade) will randomly blink somewhere. So for a system like this to work the way I would want, there would be a need to keep track of how long an item's been on the ground, a way to trigger the item changing into another item after a certain number of turns or deleting/casting a spell effect.