Good thought, bad idea.
I dont like this because you would effectively penalize WAY more people than just the Lamerkaze Leeches. What about all of the people who get headshot by a thrower or archer or crossbowman 15 sec into the round. They werent leeching, and yet there is no way to seperate them from the asshats who run in and die to soak XP. There are FAR FAR more instances of this occurring than there are leechers.
Right now, I care about having fun, and getting a better multiplier. that means team tactics and helping win.
If this were implemented, I would be more worried about staying alive, and would likely not engage much until at least half the round was over. this would make all of the rounds last a lot longer, with far more chance to draw, as people care more about staying alive than winning.