Paper Mario: Paper Mario has about a 5/10 chance I think. He has the potential to be very unique, using various stickers, and partners to attack. And that moveset potential is even greater in ssb5, with Mario & Luigi Paper Jam coming out later.
Daisy: 1/10. I think Daisy needs to appear in a mainseries Mario game for her to be included.
King Boo: King Boo's chances are about a 1/10. He is a ghost, and has control over most of the Boo we have encountered over the years along with many of his own abilities. However, he is going to need more screen time to make a name for himself before getting considered for the game. More likely in Smash 5.
Fawfull: 1/10. He is the fan favorite of the Mario & Luigi series, but he hasn't appeared since Bowser's Inside Story sooo...
Kamek: Kamek is kinda pushing it, but it's possible. He has the moveset potential though. His chances? 1/10.
Captain Syrup: 1/10. There isn't really a push for another WarioWare Inc./Wario Land character, just more game inspired moves for Wario.
King K. Rool: 9/10. He is one of the most likely character to join smash. If he doesn't, Nintendo will have made a grave mistake. (And this is coming from someone who doesn't support him.)
Dixie Kong: 5/10. Dixie Kong isn't the most requested character mostly because everyone thinks she would be a semi-clone of Diddy Kong at best. I'm not so sure, but you never know.
Impa: 3/10. Impa needs more main series roles at the moment, but she is a good pick for a series that doesn't really hang on to any characters.
Giraham: 1/10. He has to prove he is more than just a one-off (but still highly liked) character. If he gets a good roll in Zelda U, he might be a good choice.
Gannon: 1/10. People are pushing for him as well because they want a better moveset for Ganondorf. He could get in, but he needs support first.
Wolf Link & Midna: 1/10. The heroes of Twilight Princess. Probably not happening because he doesn't have enough support. Why because they involve "another Link".
Young Link: 4/10: For Young Link, it's now or never. It might happen, it might not. It all depends on how much Sakurai wants to bring back characters.
Tingle: 10/10. It's obious why he is a shoo-in.
Ok not really. 1/10. His inclusion would be funny though.
Ridley: His situation is weird. Half the people want him with a passion. The other half wants to burn him alive. And Sakurai doesn't think his inclusion would work either, so that doesn't help things. His chances? Um.......3/10?
Sylux: 2/10. He is growing in popularity slowly, but most people don't want him.
Dark Samus: 1/10. The evil clone of Samus doesn't really have much going for her at the moment. And honestly, I don't think adding Samus a third time will appease fans.
Medusa: 1/10. Medusa is dead, so I don't see her appearing again. (Unless Hades decides it would be a good idea to bring her back.)
Hades: 1/10. With how many people that liked him, I don't think Hades is gone for good. That is, if the series gets picked up by someone.
Viridi: 1/10. Could happen if there is another Uprising, but right now, not really.
Anna: Anna is the fan favorite character to join at the moment. I don't know enough about her to rate her chances accurately though. Maybe 4/10?
Chrom: 1/10. Many people wanted Chrom, but Sakurai had other plans. Robin's Final Smash.
Bandana Dee: 6/10. As one of the main four, he has pretty good chances.
Magolor: 2/10. The only other recurring character at the moment. If it stays that way, then he would have good chances for later.
Wolf: 9/10. I don't really have to say anything on this subject.
Krystal: 4/10. Krystal's popularity has dwindled, especially since they thought it was a good idea to bring back everyone but her in Star Fox Zero.
Squirtle: 5/10. See Young Link.
Ivysaur: 5/10. See Young Link.
Pichu: 3/10. See Young Link.
Zoruark: 4/10. Zoruark pretty much missed her only shot in Brawl.
Porkey: 1/10. I don't see him working without his giant spider mech.
Kumatora: 1/10. Don't think it will happen, but she would probably be the one put in the game if there was another Earthbound (Mother) character.
Black Shadow: 1/10. Only wanted to take Ganondorf's moveset.
Samurai Gorouh: 1/10. This fighter with very botched spelling will probably stay as an assist trophy.
Isabelle: 2/10. She isn't very likely, but it could happen if enough people want her.
K. K. Slider: 1/10. It would be hilarious to have a pacifist in smash. But that probably makes him less likely.
Plasm Wraith: 1/10. Not enough people pushing for him. If it appears again, it might happen.
Ryn: 1/10. Shulk will probably be the only character from Xenoblade Chronicles. (The first game, not the series.)
Fiora: 1/10. See Shulk and add spoilers.
Melia: 1/10. See Shulk.
Dunban: 1/10. See Shulk.
Riki: 1/10. See Shulk and add awesomeness.