Nowadays, the limit is 8 players. Zup already talked about the possibility of raising this limit to 10 in the next updates. So, 5 against 5 is the maximum to expect for a while, but for now this limit is 8. So, 4 against 4.
But I like the idea of "got killed, got booted" - but it would be better if the killed player could stay in the game - unable to fight, of course, just to watch it to the end. But in my opinion, the pilot should be able to parachute. Once in the ground, he could fight. Can you imagine, every planes shot down, and all soldiers walking, taking care to not waste their precious 42 bulets, waiting for the best moment to kill the enemies? It would be lots of fun!!!!
Yeah, I LOVED the idea of this one-kill thing!