Why doesn't Treyarch simply just drop CoD and focus on making a zombie experience? I'm pretty sure they'll make a HUGE amount of money, and they'd be great at doing so. It's almost very clear that a "minigame" such as zombies is more than half of the focus of Treyarch's development anyways.
Also, was it just me, or there only appeared to be 3 playable characters visible during the trailer?
If new IW/Sledgehammer didn't suck and released a well-made mulitplayer-only experience each cycle, I wouldn't mind Treyarch making Zombie games to fill in the gaps. Single player has been a throw away for me since MW2.
Treyarch switching over to full-time Zombies would be the collapse of CoD, imo. That may not necessarily be a bad thing though...
And if you want to look at it by money, more people are going to buy a single player + multiplayer + Zombies package, not to mention MP+Zombie DLC. I know tons of people who don't really care about Zombies at all. I probably wouldn't even touch it if I didn't have friends who pester me to party up >_> (it is fairly fun in those cases, though).