I would be surprised if Nintendo stuck with the single tablet as they announced it. Even if they aren't listening to everyone saying how it should support at least two, hopefully they see the multiplayer possibilities with it. I mean, if multiplayer games can't use the Wii U controller's features, then it really limits the potential of those types of games.
This is, of course, assuming it's possible. I of course don't know what kind of processing power the system needs to support four screen controllers, or even one. I guess this is why they suggested using the 3DS as an additional controller, as it could do some of the processing. I s'pose that's better than nothing, but not ideal. It'll be disappointing if it ends up with one, but if that's the system's only shortcoming, it'll still be a lot better than the Wii.