The other core part of this idea is creating illuvial weapons that you can make from illuvial ingredients and already existing materials to make cool looking and unique weapons. Such as a rhamphy/rhampyre bow, atlas gauntlets with a water blaster and so on.
While not concrete I think primarily taking advantage of the future inclusion of ethereal illuvials that aren’t capturable you could have them drop illuvial cores and other ingredients instead to be used to make and upgrade these weapons. Basically ala monster hunter. The other side could be to burn or more likely link/bond a illuvial to a weapon and transform it or something of the like. However this is just an idea based on my thoughts and hopes of roughly what the future systems might already look like.