2nd attempt with detailed reasoning
Captain Toad/ Toadette: Have their own game, were in Odyssey and are coming to the Switch.
Pauline: Just like Rosalina it doesn't take a whole lot and she's had WAY more pushes that Rosalina, Mario vs DK anyone?
Dixe: she's Dixie
Cranky: Wishful thinking but he is the original DK and was in TF
Funky: Has been in DKC and is the new push for TF
Rool: That Mii costume tells me they know, otherwise why even put it in?
Impa: Pushed in SWS pushed in HW, she's been around A lot so between her and Tingle I choose her.
Toon Zelda/ Tetra: Either or really both of them can have unique sets really
Ridley: The framework was in the last game it's there. I put him over everyone else Prime 4 could color my mind though
Ashely: Assist Trophy
Captain S: Former villain and most recent character in the Wario Land series whom might come back if that new Wario Land Rumor is real.
BWD: Has been in a ton of games and is the only wielder of the spear ability in Star Allies
Marx: Reoccuring Boss and playable character in Star Allies
Greninja's return and Lucario's absence: I'm a firm believer in this 6 pokemon to a roster thing since it keeps happening either due to happenstance or not. That being said let's talk about Battle Bond the ability Greninja got in gen 7. Now what's so important about it? Well, there's nothing like it, and that's the problem. Mega Evolution gives a pokemon a 100 point boost to their base stat total, however Battle Bond gives Greninja a 110 boost. Not only that but it increases the power of Water Shuriken its signature move, and makes sure that it will hit three times. Nothing else in the game is quite like this, my question is why? Why wasn't Lucario given something special, given all the exposure it's had, heck it doesn't even get a new ability upon mega evolving it gets adaptability which is what Beedrill gets. No unique aura related ability, nothing. So as far as gen 7 is concerned I think Greninja is your 7th gen rep and there will be news one way or another on gen 8.
Porky: the Main bad guy in 2 and 3
Plasma Wraith: Kind of is the main bad guy in the Pikmin series this is just its most powerful form
King Hippo: Fun choice, the most recognizable boxer from Punch Out, unlikely though
Rex & Pyra: Unless I get some proof, they're in.
ARMS characters: Springman and Ribbion girl are assured but here's the thing. ARMS probably needs to be in the next trailer otherwise what was said is most likely pointing towards them being added later. I think they're in because this most likely has been in development for a WHILE so yeah but there's no telling. Also the other two Max Brass and Dr. Cyole are the other two MOST important characters in the game, one being the Commissioner of the ARMS league and the other being the sort of villain figure who's responsible for a lot of things happening in the game as well as some of the equipment (The masks I think) that the fighters wear as well as being the final boss and making the final-final boss and being able to wear said final boss without issue since she made it.
Isabelle: Kind of has her own game with Happy Home designer so, eh?
Deathborn: The SUPER bad guy of F-Zero give him Ganon's set.
FE: Look man I don't know about this series take the most recent ones and shove em in there.
DJ O: Don't know how he would work but he's not very huge or awkward.
Viridi: Costume, has a shot in my eyes
Medusa: Old school villan
Hades: Really good final villan
Slippy: Is the most famous out of the four and has his own side game with Zero.
Travis: Been there since the Wii, charging his sword might be a problem but that's really it.
Labo: I believe in Labo man
Eggman: makes sense if more 3rd parties get second reps
Geno: Costume, has a shot.
Ivy: Just based on that she's popular and i find her most interesting that Nightmare who at this point would just kind of be Cloud or what Ganon turns into hopefully. Yeah, we don't have a whip user so she's cool in my book.
Crash: One of the last two legends from the 90s
Spyro: Where ever one goes the other follows.
Bomber man: Its Bomber man! Was one of the first games on the Switch.
Shovel Knight: Modern classic with a whole lot of pull and Amiibos
Rayman: Popular character that was a trophy and given a lot of traffic thanks to Smashified
Rabbid Mario: Kingdom Battle exists and its good.
Steve: The biggest thing in gaming in the last decade.