Pre-Ballot(and imo, the only potential way to get Vets):
Wolf(highly popular and easy to remake)
Snake(the ballot wouldn't be a reason to bring him back. He's popular enough on his own. He's only getting in if the licensing goes through, period)
Pichu(Easiest to make. Doesn't have issues that Squirtle and Ivysaur have. He takes not just the least amount of time, but his gimmick actually is favorable for Smash 4. Remember rage? Well, Pichu only works better in this particular game. Also, he's vastly popular, iconic, and the Gen II main mascot. Something that Squirtle and Ivysaur don't all have. They also more or less got in due to PT, not really on their own strengths. Pichu may have been a clone, but he was chosen over Raichu for a reason, who also could've been a Pikachu clone).
Post-Ballot:
King K. Rool(the costume means jack as we doing known why we got a costume of him. He's still a high contender at this point.)
Isaac(highly requested right now, but that's about it. Not banking on him, though. Would be cool, however)
Chibi-Robo(I normally would say "eh", but the new Amiibo as well as him being back in the gaming world with an all-new game makes him favorable in my eyes. Also a pretty sweet character with a lot of potential)
Krystal(still requested to this day, and has clear moveset potential as well would not have been a clone regardless. Uniqueness definitely is going for her. I consider her a fairly low chance, but still higher than most 3rd party characters bar Snake and Rayman or a Bandai-Namco rep at most. Being that Sega has no real good contenders to represented a new franchise, and i cannot see any third party franchises, who are still guests, getting more than one playable character at all)
A Bandai-Namco secondary franchise rep(Only Nightmare and Agumon do I see have a decent chance at this point. High moveset potential, most iconic enough, very popular,. Nightmare has to be a bit toned down, obviously, but Agumon does not.)
Rayman(already a trophy, has great moveset potential, only bad thing going for him is a crappy Amiibo at most. Clearly Nintendo and Ubisoft can come enough toan agreement to even make Rayman appear in Smash already. Making him playable may not be that hard. That said, I can see them refusing to cooperate too)
I already went into why I don't believe Squirtle or Ivysaur have a good chance of coming back this game, however Young Link and Ice Climbers were pretty much gone into regardless. Young Link ha snothing to set him apart from Toon Link, so unless he gets a new unique moveset that makes him feel very different, he's pretty much gone. Ice Climbers are dead due to technical limitations. This is also part of why Squirtle and Ivysaur got cut. They were only there for PT at that point, but still didn't come back on their own. There were clearly higher priorities, including Jigglypuff, which makes sense, being part of the original 12(who Sakurai has proven he views them as fairly important, although not important enough to be impossible to cut).