I think Ness'll still be around, as a really hard to unlock character, maybe?
He'll use his own versions of Fire and Thunder, share Magnet, and have Flash instead of Freeze. He'll also use his own standards attacks like he had in Melee, keeping the bat and yoyo while Lucas gets the rope snake.
Or maybe, they plan on retooling his moveset completely, giving him moves that he actually used in Earthbound, instead of taking them from Paula?