I hope they made the smart decision of not implementing these. Killcams + Instant spawning, will eliminate any form of tactics that are used, will remove the element of surprise, along with a significant amount of fun from any true Halo fan.
From a killcam, you can see where your opponent is sniping from, where he and his teammates are moving towards, what weapons they have, along with a bunch of other stuff. The gametypes with killcam enabled will be bland, easy gametypes compared to those that don't. If 343 is so set on killcams, they need to only make a final one.