Super Smash Bros. for Wii U will let you use the 3DS as a controller
Update: An image from the English version has surfaced (see below). There’s the reconfirmation of exchanging custom fighters, but no hints of any additional functionality.
A very interesting tidbit has come to light regarding the Wii U version of Super Smash Bros. Based on a menu shot found in the 3DS title, it appears that you’ll be able to use Nintendo’s handheld as a controller in the upcoming game for Wii U.
That’s not the only connectivity between the two versions of Smash Bros. Nintendo previously confirmed that you’ll be able to exchange customized fighters.
Also, while we don’t want to make too much of this yet, the way the image above discusses using the 3DS as a controller and exchanging custom fighters leaves room for even more features. The grammar structure suggests something like “among other things”.