Jig, the problem with that system is this:
If PNG took effect after ONE friendly kill, then a simple accident would result in aot being able to play the game fully. Nobody wants to penalize those who make a mistake.
However, someone who is DELIBERATELY fragging his teammates would be unaffected by that system. He could continue to land and get ammo until someone destroys him. Unfortunately, then the person killing him would himself be PNG!!
This is why I personally favor either 1. PNG requiring TWO kills, with no rearming available) or, better yet 2. Bullets simply have no effect on friendlies.
NOTE: If your bullets don't affect a friendly, there is still a "penalty" in that you wasted ammo.
J_A_B