Here is some stuff I have thought of:
On PRM, there could be a transmuter which causes any proliferation fragments which have not hit a target to slow down to a stop, then slingshot back into where they originated from. This would up its single target dps and potentially make it more viable against big single target bosses
On sky shard, I think there should be a 100% skill cooldown reduction on it with some -damage. So that you could just call them down at your casting speed everywhere like hail
Grenado’s physical damage is awkward to use with cocktail and thermite mines, which do none. I think a transmuter for a % physical to chaos damage would open up some new builds with it
A separate idea for grenado, a transmuter which causes it to become a basic attack like cadence which can trigger weapon pool skills. It transforms your gun into a grenade launcher which launches at half your attack speed, with half the attack speed cap.