I'm posting this information to see if any of this actually comes true. Obviously take this with a huge grain of salt because I don't know if any of this is true or if this guy is a big liar. In the Bay Area the smash scene is pretty big. In SF, they hold smash gatherings every week (In Oakland as well "the Made"). Tonight there was a guy who says his internship with Nintendo had just ended. Yes, Nintendo has an office of some sort in Redwood/San Mateo (Bay Area). Anyways, I'll just share the basics to keep it simple.
The following chars are supposedly to be revealed
Bowser Jr. and The dog from duck hunt
Not returning/added:
Wolf and Mewtwo
*49 chars total
multiple skins available such as Dr. Mario. and Jr. Bowser's alt. costumes are the koopa kids.
I'm not standing behind this guy by any means, but we'll see if any of this comes true.