What about Dedenne? It's basically the little Pikachu of this gen just like Pichu.
But even then he didn't say Greninja, he was vague as fuck and guessed that a 1 Pokémon from over 70! will join the roster.
If you believe him for that then I guess I will go ahead and put 70 characters on a list and predict that "a character from this list" will be a newcomer.
I totally believe his first leak, but there's no proof for his second leak until Shulk or Chorus guys are revealed, (Pauletena and Chrome are highly likely).