Combining weaker addons
Many addons follow a system where they follow a trend of "same effect, higher rarity = higher potency." Meanwhile many would argue that the weakest versions of these addons have a very underwhelming effect, and end up sitting in the player's inventory by the dozens. It would be nice if there was a way to combine them to make a higher level version? It could even be done in two different ways: combine 4 of the same to get the next level in the same type, or two of the same tier to get a random addon of the next rarity, something like that.
Basically we need a horadric cube for addons.