Today, Nintendo announced that thew new Smash Bros. for the Wii U and the 3DS will be developed by Namco Bandai Games and Namco Bandai Studio. Masahiro Sakurai is helming the project. Of course, Sakurai's studio, Sora, will be assisting in development.
Namco's Masaya Kobayashi, who's worked on Ridge Racer, and Yoshito Higuchi of the Tales games, will be developing the game on the Namco side.
There is a precedent for this. The most recent Smash Bros., Super Smash Bros. Brawl, was developed by a handful of studios, too, such as Monolith Soft, Paon, and Game Arts.