I think a survival mode (not exactly zombies) would be pretty cool in MW2. But I seriously doubt they would add that if they are having Special Forces mode. I think they added that to replace zombies. I don't think they wanted to put zombies into MW2 because it would just look like they were copying Treyarch, which is exactly what Treyarch did to Infinity Ward. However, I hope that the Special Forces mode will be really fun. And I guess if MW2 doesn't have a survival type game mode then I will have a reason to keep my WAW because honestly zombies is the only reason I even get on WAW now and is the only reason I bought both of the map packs.
Theres always that speculation when the next game in a sequel comes out. I mean I would like to think that they would have some sort of arcade/challenge on it but who knows. I hope its like Horde on Gears 2. Where there not mindless zombies who just sprint at you. I want them to have some sort of intellagence.