We know that Super Smash Bros for Wii U and 3DS won't include a Story Mode, thanks to game director Masahiro Sakurai's frustration with story scenes getting out on YouTube. That doesn't necessarily mean it won't have a single-player component, and a new screenshot may have given us a first glimpse at it.
The stage appears laid out similar to the Subspace Emissary from Brawl, to the point that Sakurai apparently felt he should explicitly remind us that it isn't. It notably only shows one character (Mario) and some platforms. Keep in mind, Sakurai was annoyed with story beats getting out, so a less story-focused single-player mode with similar level layouts could still be in the cards. We probably won't know for sure for a while, though, as Nintendo has been drip-feeding tiny bits of information like new character reveals for months.