Mastery skins for the RPG, talon, repair tool, drone, C4, grenade launcher, supply pack, health pack, stim gun, defibrillator, Zipline gun, proximity sensor, and respawn beacon.
For the RPG and talon, they could be achieved by damaging and destroying vehicles, the repair tool could be achieved by repairing vehicles, the drone by repairing vehicles and zaping enemies, the C4 and the grenade launcher could be achieved by either kills or destroying vehicles, the supply pack by giving ammo to your team, the health pack and stim gun by healing your team, the defibrillator by reviving teammates, the Zipline gun by people using your Zipline, the proximity sensor by sensing enemies, and the respawn beacon by respawning teammates.
I think this would be a neat addition that encourages people to use their utilities to help the team.