Ever since Super Smash Bros. for Nintendo 3DS was released, fans have been rooting around in the game's files, finding pictures, textures, and a lot of text.
A Smash fan who goes by the username PushDustin has translated many of the files and come across some interesting language, including text that suggests the game will support DLC.
Other findings include textures for bosses (Ridley from Metroid, Metal Face from Xenoblade Chronicles, and Nabbit from Super Mario), a DLC shop link for the game's main screen, and text suggesting the 3DS will be used as a controller for 8-Player Smash in Super Smash Bros. for Wii U.
Perhaps most interesting is that the game is set to display the text "A Challenger Approaches!" when connecting Super Smash Bros. for Nintendo 3DS to Super Smash Bros. for Wii U, though whether this means connecting the two will unlock new characters, or it's simply a message indicating a successful connection remains to be seen.