What I would really want in Grim Dawn is something from days long gone of Diablo 2.
A Horadric Cube.
Can be renamed to some Eldritch Horrors Case and run on Dynamite(
cause why not).
It could handle a new way of equipment upgrade like merging two of the same unique items into one more powerfull, or merging two different uniques of the same class to completely new one with stats randomly picked from merged items.