I don't think you'll be fighting an army of zombies or anything like that. I believe the sub story of 115/zombies and the main story of Nova 6 will merge and zombies will be used as some sort of weapon. I put together my hours of research why I think the new game will be based on zombie warfare.
Just from reading the clue at the start, its aimed at killstreaks in MP. You will be able to infiltrate the enemy team for a certain amount of time, Zombies will be seperate like always. Just my opinion