Isabelle (
Animal Crossing series)
Chances: 95%
If Isabelle is not playable, I will be completely shocked. She has so much going for her; popularity, promotion, prominence, possibilities. Her series is a big one of Nintendo's and she's been pushed heaving as a sort of mascot for it.
Her chances I'd put above anyone else's, because not only does have all these strong points in her favour, she also has Echo potential. I personally believe she'll get in as a character with a unique move-set, but the fact that she even has the alternative option of being an Echo is strong argument for her gaining a playable role, regardless of how that is.
Want: 56%
I'd prefer Tom Nook, but Isabelle is a pretty deserving character for inclusion and Animal Crossing is a pretty deserving series for multiple reps. This Want will probably be a lot lower if she is an Echo; I feel people pass on her potential for a unique move-set too easily (though I feel that is my problem with the introduction with Echoes in general). Aside from that... I'm not a fan of Animal Crossing but she is a cute character and a Nintendo one at that who'd allow an under-represented Nintendo series to gain more representation.
Shadow (
Sonic series)
Chances: 68%
I think I may have rated Shadow a little lower than others here, but I tend to make these rate their chances without looking at other people's ratings first. Now to be clear; this is in regards to Shadow having a role as an Echo fighter, as I highly doubt he'd be included as an original character (so far the only 2nd rep from a 3rd party series is an Echo, so I'm using that as a limiter until proven otherwise).
I'm assuming everyone will have gone over why Shadow is likely; he's an easy Echo, popular, fits a rival theme that seems to be a popular belief as of late, has a character distinct from Sonic that can be expressed through taunts and such, no costume confusion, etcetera. So instead I'll talk about reasons why he might not be included. For starters, the whole Simon/Ritcher thing might be a special exception, given that Simon's move-set takes a lot of inspiration from Ritcher. Shadow also has competition for the Echo spot from the likes of Tails, and despite fitting as a rival to Sonic, Shadow doesn't fill in a villain spot or anything like the inclusion of Ridley, King K. Rool and Dark Samus.
My final reasoning as to why I believe Shadow isn't as guaranteed as a Sonic as others believe... I'm pretty Sakurai hates Sonic, or at least doesn't care for him. Just look at all the love and dedication that has gone into the other 3rd party inclusions, particularly Mega Man and Simon Belmont, then look to Sonic. His move-set is bland, consisting of mainly variations of his spin attack rather than other potential moves such as Light Speed Dash, Sonic Wind/Blue Tornado, Bound Jump/Bounce Attack, Super Boost, and many more. Even his alternative costumes are boring, with it being difficult to tell them apart in the midst of battle. I just don't think Sakurai cares for Sonic quite like he does some of the other 3rd parties in SSB. I still think Sahdow's chances are in the realm of more likely than not for inclusion, but if other 3rd party Echoes get included such as Roll or Ken... I wouldn't be surprised.
Want: 25%
I like Shadow... not as much as I used to (Sonic Adventure 2 and Heroes was good... I'd have liked him being a robot clone, that was a cool idea), but I like him. I don't like 3rd parties in SSB, nor am I a huge fan of Echoes; though a 3rd party Echo is pretty much the only way I feel comfortable with the inclusion of a 2nd rep for any of the 3rd party series represented in SSB as it doesn't take development time away from the Nintendo characters. If he does get included, I hope he at least has Chaos Spear; love that move.
I've so many I want to see nominated for rating, but I doubt I'll get more than one at this rate... ah well, you know who I'm nominating:
Nominations: x5
Fatal Frame Protagonist