It exists in other multiplayer games such as the new Counter-Strike, but how well do you think that a Lab type in Uncharted 3 where the first player in a free-for-all match to get a kill with every weapon would do?
Every player would start with the same weapon, and every time they got a kill, the gun would upgrade to another. It would start with the pistols and then go to the Long Guns before ending up with the Power Weapons. Perhaps remove blindfire and melee damage to prevent BF+Punching kills?
So the gun rankings would go like this from least to last:
1. Para 9
2. Arm Micro
4. Tau Sniper
7. Dragon Sniper
13. Sawed-off Shotgun