Okay, so Kotaku posted leaked screenshots of potentially the entire roster (minus DLC characters) for the next game. Among the characters shown that have not been revealed yet:
THE FUCKING DOG FROM DUCK HUNT
Shulk from Xenoblade
Bowser, Jr.
Ness
R.O.B.
None of this has been confirmed by Nintendo, but it's pretty clear there. Also, this is Kotaku and the author of this particular article didn't run the story until he saw video evidence of it.