To be perfectly honest, I feel that if they're going to be expanding on the idea of alternate costumes such as wire-frame Little Mac and Wario's classic costume, Lucas would probably be best suited to being an alternate costume for Ness. It would be a good way to keep him in the game without taking up a character slot with someone who (IN MY OPINION) didn't feel different enough from Ness to warrant a separate slot on the roster. The same thing could probably be said of the Star Fox characters if Sakurai really wants to weed out the excess clones from the roster (though Toon Link still made it in, so there's still the question of if that's even one of his goals with the game).

I would figure that Ninten (protagonist of Mother 1/EarthBound Zero) would replace Lucas and have a more unique moveset. I have a whole list of counterarguments in case one were to bring up the fact of him and Ness looking too similar.

But again, Ninten could make a great Ness alternate costume. There's no doubting the leak at this rate since the majority of characters have been confirmed so far. We definitely know the Chorus Men will be in due to a Rhythm Heaven enemy appearing in Smash Run.