Notes:

Dix could be an echo of Diddy with a different move or two to utilise her hair. She could be more unique but you could also say that of Daisy and Dark Samus, though I guess it's also possible they could revisit the Brawl idea of tag team Diddy/Dixie but with like Kiddy instead? Isabelle and Shad are very expected though I hope Tails is in there too at some point, having gotten a Mii costume alongside Knux (who got an assist) and being significantly more iconic and important. Having come real close to getting a Rhythm Heaven rep in Smash 4 (emblem, Smash Run enemy, Gemetsu), I hope they deliver this time. Rayman had a couple of leaks of at least lucky guess-level accuracy and is the mascot for a company doing several crossovers with Nintendo, not to mention a requested character back in the day (Arsty Omni leak). Maybe Black Shadow could be like Melee Ganon, and his inclusion would finally give Falcon a clone for his own series. Perhaps after bringing it up in the Smash 4 era, Sakurai reconsidered trying to implement a moveset for Heihachi, with him being referenced in Ryu's character trailer. I'd pick Balloon Fighter for the retro rep but we kinda have his shtick still represented in the Villager's up special. Maybe 9-Volt could be a fighter representing Nintendo in all of his moves, albeit probably pissing off Ashley fans in the process.