Here's some food for thought.
Early in SSB4's development, I remember a quote from Sakurai stating that, at that point in development, all characters from Brawl were in the plans, but cuts are (or, were) a definite possibility. If anyone could back me up on this and find said quote, it'd be much obliged.
Now, this really doesn't mean too much for me, but it raises one or two questions. I'm assuming that Squirtle and Ivysaur were scrapped, with Charizard being the more acknowledged of the trio, and they just considered that the best option. Lucas was probably taking too long to develop, so they pushed him to post-release, and Icies were just struggling on 3DS, so they scrapped them.
Now, that leaves Snake and Wolf up in the air for me. Both have popularity, both are capable of running on 3DS smoothly, and are unique enough to bring back. So, why were they absent in the first place?
IMO, I think Wolf was in the same boat as Lucas, taking up development time or something along those lines, and was pushed to the side for later. Personally? I think that Sakurai pushed Wolf / Lucas away for later development because they were still considered "semi-clones" (I know they're not, I've played my fair share of both) and neither really had a foreseeable future, with Mother and (at the time) Star Fox being dead franchises, so why focus on them over more popular veterans and newcomers? I don't know if, in this case, that would mean Mewtwo / Roy / Ryu had priority over Wolf for some reason, but w/e, I'm fairly confident if we do see a character alongside the Mario Maker stage, it'll be Wolf. Either that, or they'll wait for Wolf to coincide w/ Star Fox Zero, like how Lucas coincided w/ EarthBound Beginnings.
Now, that leaves Snake. I don't think Sakurai would just decide to cut a character that famous among gamers... I mean, yeah, he's done it before with Mewtwo in Brawl, but to be fair, he was scrapped rather late in development. I believe that Konami, or maybe even Nintendo, denied access to the Metal Gear Solid franchise, forcing Sakurai to remove Snake. This means, to me, that he's probably not showing up soon unless the Ballot really shows how much we want him. It just doesn't add up to them holding back someone who is the sole representative of his home company, and doesn't appear in the base game.
That's just my two cents, though. I'll just go back to wishing that SEGA Carnival stage was real, with After Burner II and Segata Sanshiro as tracks.