The new Super Smash Bros will release on Nintendo 3DS and the newly revealed Wii U. President Satoru Iwata explained in the E3 press briefing that game developer Masahiro Sakurai is onboard with the project.
From Shacknews
“A few months ago I explained the concept of Wii to Mister Sakurai, who was developing [Kid Icarus: Uprising],” Iwata said. “We were discussing which platforms his next game should be developed for–Nintendo 3DS or Wee U? What Mister Sakurai suggested then was an idea to make Smash Bros. for both Nintendo 3DS and Wee U, to make it work together on both platforms.
“Since his team is still involved in the final work for Kid Icarus maybe I shouldn’t go into any detail today, but I think I have just promised you that Smash Bros. will be developed for Nintendo 3DS and for Wee U, and that the software will work together in some fashion.”