Notes:

Now, before you go all out spouting "FAKE!!1one!" and thumbing this down; hear me out.

The second last line said here is the announcer saying "Smash World!"
Back in late September, the leaker listed this Smash World game mode as a feature coming to the 3DS version once the Wii U version is released.

Not only will Mewtwo, Impa, Ridley, Chorus Men and Dixie Kong be coming, but so will Isaac (so finally people can shut up about wanting him in) and Wonder-Red.

"A new ink blaster item will be added, a brand new Splatoon stage awaits your arrival! And maybe a special guest will appear to battle!"
So, some Splatoon-related content… and an Inkling being playable or an assist trophy? I think the former since "appear to battle" sounds very playable character-like. I'm taking the Isaac, Wonder-Red and Splatoon things with a grain of salt. It'd be a pretty neat mind-blower if it turns out to be true, though.

EDIT: Turned out to be lies. The Wonder-Red, Isaac and Splatoon part at least. The Smash World thing, however, could still happen since there's the audio file to prove it.

inb4

Another day, another controversial upload.