If one is coming I can't see it being released anytime soon especially with Ghosts coming out. Alot of the attention has been moved to Ghosts and the zombie hordes have been teased by a possible similar scenario but 'vs Aliens' survival mode.
If there was to be an update it may come a few weeks or months after Ghosts is released.
Nevermind, it wasn't deleted haha. For some reason some of my replies havent been showing up. I just checked that same thread and it was there this time. Who knows honestly. This forum has been super buggy since the last site maintenance.