As others have said, you can't judge the mode yet, as no real information has been released yet.
I in a way see how it can work, and cannot work well... Though it would be intresting to see how they have this worked out, and regardless there should (hopefully) still be a regular zombie mode for just 4 players/solo.
Time will tell.
Treyarch did say that there will be eight player loobys.
Kevin Sherwood (who makes the music for zombies) posted on his youtube page to check out and artcile and it was talking about the major changed to zombies that Treyarch is doing and one of them is adding eight players.
I'm pretty sure it isn't just 8 player. I'm sure there are going to be options for you to choose from. I remember hearing or reading somewhere that not only will there be the 8 player co-op, but also team based games as well as the classic 4 player game type.