Cranky Kong and Dixie (Tropical Freeze)
Bandanna Dee (Kirby's Rainbow Curse)
Waluigi and Daisy (Mario & Sonic at the Rio Games/Mario Tennis Ultra Smash)
Elma and Cross (Xenoblade X)
Paper Mario (Paper Mario Color Splash)
Wolf and Slippy (Star Fox Zero)
Chrom and Tiki (Tokyo Mirage Sessions #FE)
Toad (Captain Toad's Treasure Tracker and Super Mario 3D World)
Inkling (Splatoon)
Midna (Twilight Princess HD)
Lana (Hyrule Warriors)
Monita (Nintendo Land)
Rayman (Rayman Legends)
Am I missing some?
Now, IMO, the characters there that are unlikely are:
-Cranky: Because Dixie and K. Rool are much more popular.
-Waluigi and Daisy: For being not very important, the Mario sports game are not considered important for me, also, Waluigi is an AT.
-Cross: Because Elma is more popular (and more important to Xenoblade X? that's what some people say, I didn't play it).
-Slippy: Because... why?
-Chrom and Tiki: I don't know, more FE would make me explode, but even if that happens, the newcomer would have to be someone from the new game IMO. (Fates or that remake or whatever).
-Midna and Lana: One is an AT and the other is a character from a spin off, also Breath of the Wild is so popular that it will probably take priority over the older games.
Now, the reasons for the ones that are likely, IMO:
-Dixie: Her role in Tropical Freeze is good and she is a very iconic and popular character.
-Bandana Dee: Dee
is a shoo-in 's role in Rainbow Curse is fine considering Dedede and Meta Knight didn't get one, and even if Rainbow Curse is some kind of spin off, it's the only Wii U Kirby game. Also he is popular and all that.
-Elma: She is fine, not unlikely IMO, but I'm not sure if that likely, specially with the new Xenoblade game coming.
-Paper Mario: He is very likely for me, Color Splash and Paper Jam gave him a very big boost in recency, popularity and moveset potential (paint and copies). The only bad thing about his chances is that some people hate the new games and/or the possibility of another Mario as a newcomer (even if it is obvious that they are different characters and wouldn't be clones).
-Wolf: Yeah... popular veteran.
-Captain Toad: Toads are very iconic and popular and this guy had his own game.
-Inkling: Splatoon was a huge success and yeah... they are basically confirmed.
-Monita: The next WTF character like Wii Fit, yeah, I know those fan made rules for types of characters are not real, but still, Monita as a newcomer wouldn't surprise me
that much.
-Rayman: Popular and iconic third party.
You forgot a few.
Isabelle and Tom Nook (Animal Crossing Amiibo Party)
Yuri Kozukata (Fatal Frame Maiden of the Black Water)
Shovel Knight (Shovel Knight)
Shantae (Shantae: Half Blood Genie)
Tetra and arguably Tingle (The Legend of Zelda Wind Waker HD)
Possibly Steve (Minecraft)
Hunter (All Wii U Monster Hunter games)
Jill Valentine or Chris (Resident Evil Revelations)
Don-chan (Taiko no Tatsu-jin)
Heihachi Mishima (Tekken Tag Tournament 2)
Ryu Hayabusa (Ninja Gaiden 3: Razor's Edge)
arguably Party Phil (Wii Party U)
Yukimura Sanada (Warriors Orochi 3)
Wonder Red (The Wonderful 101)
Jibanyan (Yokai Watch: Just Dance Edition)
Tails, Eggman, and Knuckles (Sonic Lost World and Sonic & All Stars Racing Transformed)
And for this group... basically all of them are unlikely XD... again, IMO.
Some are super niche, some are indies, some lack popularity, some already have roles in the game (assuming it's a port, that's very bad).
Tetra, Wonder Red and Jibanyan are probably the ones that are not that unlikely from that list, for me.