It's most likely going to come with a Wii-remote and nunchuk as well, expect some games to use those as the main controller.. As for the number of touchscreen controllers, that's unknown. The original announcement only had one of those supported per system, and there were no plans whatsoever to sell them separately. When pressed, Miyamoto said they were going to look into if it were possible to support two of them on the chance that a third-party developer might want to have a game that required taking your controller to a friend's house.
I hope they can make the effort to support two Upad, but I don't see in a "Upad + Remotes" scheme a limit.
I think that it's main focuses will be on single player experiences and online multiplayer experiences, in terms of direct control.
About the local multiplayer, I think that they will stress the a-simmetric scheme, that in my opinion could be a very new way of handling that part of the game.
Yes, probably we will not be allowed to play locally with 4 Upads, but considering how that could cost and how interesting could be the asimmetric method, I think that this solution could offer a lot.
Upad = single player
Upad = online multiplayer
Upad + remotes = local
In this way, it can be easier to setup (cheaper in terms of costs; a lot of remotes all around the world and the backward compatibility should help this part; new game modes and so on) a very interesting local multiplayer up to 5 players (and not only 4)