Not 100% sure. But, they have released new info on it. It's going to be like Call of the Dead. It's called Mob of the Dead and it has all new celebrity survivors. That's all that's known for now. A trailer should be coming out with all the info within a couple weeks.
My guess would be in the next few weeks. They will most likely be releasing the next trailer next week sometime. If you watch YouTube, go look up TheSyndicateProject and NGT Zombies. They only do zombies, but they talk about the Mob of the Dead in the new DLC, and Syndicate said that this map was most likely legit and that the trailer would come out soon. Also if you have a Twitter I highly recommend following David Vonderhaar and a few other guys from Treyarch over there. They release information about everything: new DLC, Double XP, Nuketown 2025, things like that. Hope this helps:)