I feel like no one can accurately predict who the final character will be. Like, I think it's gonna be a Pokémon, but I have no clue who exactly it will be. I'm guessing Cinderace, but what I learned from Ultimate's base game is that even if a certain Pokémon seems like a lock, it doesn't necessarily mean it is. though i was personally never in the "decidueye is a lock" camp despite how much i wanted him.
So here are my thoughts on Pokemon chances. Cinderace is strongly in the lead, but Rillaboom and Inteleon are close behind.
I actually think Urshifu would be a very reasonable choice and be amazing to play as.... but then Kazuya was revealed
Not sure how the fanbase would react to Gruff Martial Arts man into Martial Arts Bear thing. Still, don't be surprised if Urshifu makes it into a Smash at some point.
Toxtricity, Grimmsnarl, and Dragapult I think would be the next best choices from Gen 8. Just imagine how hype a Gigantamax Grimmsnarl Final Smash would look like
Toxtricity has the punk rocker vibe going on, Dragapult would just be unique on movement alone (and shooting mini dragons).
Sir Fetch'd is funny to imagine just because "Oh no, not -another- anime swordsman..."
After that are Pokemon that sort of missed their shot like Zeraora, Decidueye, Gengar, and Machamp.
One Pokemon that's under the radar as a Fighter choice, in my opinion, is Melmetal. One area for representation for Smash that could be neat is Mobile. Well, you could combine mobile, Pokemon, Pokemon GO, all in one roster selection! My only concern with Melmetal is.... what music would you choose? Does Pokemon GO even have that much music? Would they just pick Gen 8 music to go with it instead?
Also with all the Sinnoh games coming out soon, Gen 4 Pokemon stocks could be going up. Is that a Garchomp joining the roster in the distance I see?