Personally I think any tech is going to have a hard time streaming a lagless display to more than one device. Remember how bad the PS3/PSP remote play feature was even when in the same room as the PS3, and that this device has a much higher resolution, I just don't think streaming full gameplay video to more than one device is feasible. At least without a lot of lag or dropping frames.
I think most WiiU games are going to use the remote or classic controller pro for local multiplayer (which i think is an AWESOME controller btw) or be designed for one Tablet Controller player and the other players use remotes or classic controllers.
Then again peter moore did mention using it for playcalling in madden and stuff so maybe it will work to have 2-4 tablet controllers connected if the display isn't a full gameplay feed, just some interactive/static menu screens. I still don't see anyone buying multiple tablet controllers. They'll probably be $75 or more.
I've seen a lot of complaining about only one tablet per console, what does GiantBomb think?