Don't know if any of this has been said already but; A completely seperate ranking system just for zombies which could be used to unlock stuff like activate different perk machines for you or start off with better weapons or be able to pack-a-punch etc, bigger and more complicated maps, a few more drops..but nothing stupid, the ability to alter game settings (so like halo 3 custom games but more extreme (modding style

)) in private matches, and as many guns as they can squeeze into it.