Please do not make it possible to instantly respawn in objective games such as assult and CTF.
Instant spawning can only really work in FFA gametypes and slayer. In slayer, instant spawns can work because it will be harder to get tight map control with everyone spawning so quickly, so gaining it will be that much more rewarding. When one person spawns back to back and gets sniped twice in the time it usually takes to get sniped once, then it is twice as rewarding. FFA might be okay with instant respawns because there never is any map control for FFA.
This is all pretty heavily reliant on the spawn system working properly in Halo 4. It needs to be able to give you safe spawns, yet players should be able to predict your spawn with a fair amount of accuracy.