It appears that there will be a separate Charizard character, rather than Pokemon Trainer. It looks like Zero Suit Samus may also be as separate character this time.
A new character has been introduced. That is Greninja (Gekkouga is his Japanese name, as can be seen in the URL for the character intro page on the official SSB4 website). I have no clue who this is, but he appears to be a Pokemon, going from the fact that the official page that shows him shows a Pokeball near him. I have no clue what season he's from, but he must be one of the latest Pokemon in the series.
Here's official artwork for the Greninja SSB4 update found on the official SSB4 website.