I just thought of something - If players join in at the middle of the game, they won't have gotten any point - perhaps they should start out with the average of the other players score?
I feel a bit that this would add some slightly artificial rules to an otherwise natural game. On the other hand, one thing I like about this one is that it would give the game a natural rythm. I remember a real-time strategy game called Tone the Rebellion which had some kind of natural change of seasons. So did the game Empire of the Ants. (which, and this is real offtopic, were inspired by an okay book by Bernard Werber)
The experience of the game could be varied a great deal by different timers: in one game, The timer would count down from 10 hours, so the teams would have to aim for killing each other instead. In another game it might be every 30 second, and every 0.1 sec in another. Or the timer is set to run out just the moment before the game ends.
There should probably be some kind of visual showoff when the counter runs dry - some sound, slowmotion, or maybe the screen gets toned with the color of the winning team.
I wonder if we could combine the countdown and the games timer into some cool GUI?
Yeah, else it would pay off to die just to get respawned with some more points. We could also let everybody else get a point when someone dies. Gameplay-wise, the result would be kind of the same as taking one point from whoever died.