I definitely piggyback with both @Tac's and @Agame360's suggestions. Great idea BTW. I usually don't bother dusting off the mic unless I'm playing with friends anyways. But when it comes to Zombies, the lack of any communication with randoms makes the game pretty hard sometimes.
That being said, I'd like to revive some of my own ideas from the past I'd like to see implicated in some way. Those being:
More "Scare Factors" added to the environment and feel of the maps. (Much like Verruckt) to keep you on your toes. Treyarch is already known to mess with our minds with cryptic messages. Now lets see them mess with our eyes and ears!
A ranking system. I tried a mod for this via WaW on PC and it basically was getting XP the same way you do on MP, but on Zombies. They brushed up on this a LITTLE bit in Blops 2, but not much. I feel for me personally, the sense of being awarded and making progress with each and every game is ultimately what will drive me to keep playing that mode. This goes for damn near any game really. The fundamental feature for addiction in games starts with earning XP. I'd love to start seeing some daily/weekly Zombies challenges along side progress and stats for playing zombies aside from just the overall leaderboards.
Randomized/Interactive maps. I always thought it was cool how some maps, the perk machines weren't always in the same location each and every game. I'd love to see that taken an extra mile for at least one map where even the series of events and when "special zombie" types spawn or happen so it's like a different experience almost every time. Best example I can come up with is a system similar to how Left 4 Dead works. Special Zombies, especially the Tank or Witch is hard to guess just when might appear and where. It's never the same exact spot. It may be with in a certain general area, but never the same exact spot and it switches up between the Witch or the Tank. I'd like to see them do that with not only the progress of Zombies, but with the map itself as well. What if it were to randomly start raining for a few rounds? Or snow even? Perhaps a line is cut and the power is shut down for once, leaving everything disabled? Things like that too.