Well that's interesting game concept. Wonder if they'll put all Fighting types in? Would definitely fit the theme and there's a variety of styles represented- except maybe they won't use the Musketeers since I can't really see them in a fighting game as quadrupeds. Unless they pull a Motaro from Mortal Kombat.
Just some speculation if they ever do all the fully-evolved fighting pokemon as a roster and the roles they could do:
Grappler/Counter-
Throh, Hariyama, Pangoro, Emboar, Scrafty, Chesnaught , Heracross (some strike-based horn moves)
Shoto-
Lucario, Mega Mewtwo X, Poliwrath (Water gun moves + maybe some grappler moves)
Rushdown-
Primeape, Sawk, Mienshao, Blaziken, Infernape, Mega Lopunny, Machamp (slower but emphasis on many arms I'm guessing)
Zoner-
Conkeldurr (pillars would have big range), Gallade (Teleport Mix-ups/extendable blades/Psycho Cut)
Technical/Special mix-
Hitmontop (mix-up/combo-heavy/some counter)
Hitmonchan (speed/maybe some counters)
Hitmonlee (maybe zoner with the stretchy legs)
Hawlucha (aerial-focused, speedy grappler)
Toxicroak (maybe some counters like Revenge/Sucker Punch?, poison counters)
Meleotta-P (stance-based character- more combo-friendly as Pirouette, maybe projectile zoner as Aria forme)
Breloom (some strike-based rushdown moves like Mach Punch, some counters, Spore/Bullet Seed projectile.)
Medicham (Teleport zoner, charge moves?)
Charge-
If any of them had to be charge characters they would be the more defensive ones: maybe Scrafty or Chesnaught? Maybe Sawk/Medicham for a faster charge character with sudden bursts of combo moves. Heck, Hitmontop can possibly fill this role as well since it seems like it's mostly in a defensive position. Breloom another possibility with some utility moves, maybe like Mitsuru from Persona 4 arena.
Maybe even Tyrogue as a joke baby character.
It would be neat to have those good range of styles and any other types would be a nice surprise. At the very least if they have Heracross I feel Pinsir should be in it to go with the dual beetle battle theme and it mostly learns Fighting moves. Would love to see things like Scizor, Bisharp and Kabutops as well. Maybe special item using Pokemons like Marowak and Farfetch'd joke character could make a suprising cut. Knowing Tekken's Panda and Kuma characters, Bearctic and Ursaring could be possible.