This is a nice-to-have, but I have no idea of how complex it would be to implement, or if it is even possible in the current game engine design.
Often I have themed characters that I have spent a lot of time on the illusions to get their final fixed costume look. When you find a new item to equip you still need to go to the illusionist after setting components and augments, and sometimes you may have destroyed the old item and cannot remember what illusion you actually had on it. If there was an toggle option when you set an illusion, say on a chest piece, that could make it persistent (or as another term “sticky”) to that SLOT, then when ANY item is placed in the slot, it would automatically take on the sticky illusion. I know that illusions are bound to the item, but they are easily removed with “Illusion-be-gone” flask from Kory, so any auto illusion added when you add to slot can be removed without issues. This is not a game-breaker if not possible, but the players who play in RPG character mode really would appreciate this to keep their “characters in character” when finding new upgrade items.