IF we get ken incineroar soon here (like next week) and that isnt the end...
i'd guess Geno or Sora or maybe Steve? for the final directs "big" character reveal (maybe a dragon quest character instead, whatever the square rep is).
probably an echo or two left as well: shadow/dixie make the most sense to me (i think dixie is better represented as an unique fighter and not as an echo but shes the final really deserving purely nintendo character thats not in the game in any form yet and her as an echo just makes her easy to include). theres also impa, medusa, black knight, and black shadow who all have some what of a chance imo (potentially hilda/octolings but im leaning more towards no on those).
theres a few other characters who might surprise us and make it in (if we do have a few more beyond ken/incineroar) waddle dee, elma, isaac, skull kid, rhythm heaven rep, maybe paper mario... some of these might be held off for dlc, some just might not have made the cut, but MAYBE one of them made it in base roster.
theres a few other potential third party characters: heihachi/lloyd for a second namco rep, rayman has a shot, same with shantae, maybe banjo if steve isnt playable but just minecraft "content" in smash so microsoft is on board. i feel most of these are more likely dlc choices than base roster right now though. shantae might be an assist trophy too(if shes in at all), also dante MAYBE has a chance base roster if matt walker was straight up lying when he said "no dante" but im not at all holding out hope for him.
I obviously dont expect all of this or even close, just laying out who i think is "possible". I feel like best case scenario is like 5-6 fighters more likely 3-5 though (with of course box theory ken/incineroar and thats it as the absolute worst case scenario).
best case scenario might look like: ken/incneroar/geno/shadow/dixie/waddle dee (though admittedly steve? is more likely than waddle dee i just think best case scenario is minecraft is a stage/assist trophy and not a playable character but thats my personal preference).
middle ground would be like 4 more: ken/incineroar/shadow/geno or something close to that (or go with like dixie/sora if you prefer over shadow/geno) a single unique newcomer and a single unique echo for two more reveal cycles. This is if the square rep is in base roster, otherwise it could be Steve? and an echo for the final reveal though i feel thats a controversial final reveal so im leaning towards "minecraft content" and not playable steve? at the moment.
worst case is of course: ken/incineroar and thats it. though i think even then the square rep is either a surprise reveal for the base roster at the end OR revealed as DLC before launch.