I’m thinking this would be more for weapon runes (rather than utility), but imagine that it costs a gem socket on your weapon, but each gem type can alter certain traits of a rune attack instead of a general weapon buff:
Change/infuse elemental type
Reduce focus cost/spend stamina instead
Add life steal
Recover poise on cast
Speed up attack animation/shorter wind-up
Increase damage
Increase poise damage
Increase size/reach
You get the idea.. prolly couldn’t make a function for every gem type, but I think as long as a weapon rarity keeps it’s respective gem count, could be a cool twist to an already fun way of making a weapon your own.