I think it's safe to say that Lucario was our first legitimate anniversary character. Why he was picked is unknown, but it could be because the developers liked him over other characters.
I'm starting to wonder who exactly will be cut at this point. Lucario was one of the most suggested as a cut. Sakurai isn't planning cuts necessarily, and we know that nobody has been cut so far. (If that is what he means btw, that means Snake is automatically back).
Lucas is similar to Ness by his specials, but aside from that, he's pretty unique. Ike is in his own class of swordsman, and was incredibly liked for Brawl. Falco and Wolf are popular, and could easily be decloned even further (not saying Wolf is a clone really)
Wario, Yoshi, Diddy, Falcon, Ganondorf, Ness, Meta Knight, Jigglypuff, Ice Climbers, G&W, and R.O.B are in my opinion for sure in this game. Call it a hunch, and the fact that they are pretty damn likely.
I don't see who you cut. I mean maybe if you are forced into cutting PKMN Trainer because of technical difficulties, that's 3 characters right there. If 3rd parties coming back is a universal thing, then that means Snake is back (which I'm pretty sure he will be for multiple reasons).
Therefore, at this point, Ike, Lucas, PKMN Trainer, and Snake are the only characters I see as potential candidates to be cut. At least that's my point of view.