if you come up against a decent organised team they will make sure you never even leave your spawn once they killed everyone on your team a few times as they will push you back, it might be just 3 sec's, but in those 3 sec's they can move up and push you back further, and once you're pushed back far enough those 3 sec's is more as enough time to reload to make sure they're ready for you coming back again
sounds nice in theory, will be hell if actually implemented
people will do anything to win, so what makes you think they won't abuse the respawn timer ?
most of the spawnkilling happens in CTF, which has a 7.5sec respawn delay
doesnt take a rocket scientist to figure out that that respawn delay is one of the biggest factors of it being possible to trap people like that