Well right now the most realistic Pokemon game for the Wii U is the fighting game, that they already hinted at back in August.
The fact the trademark for Pokken Fighters was made after that, points heavily to it being made by the Tekken team with similar gameplay, and after Hyrule Warriors was recently announced, it's only a matter of time before this game is offically announced as well.
There are currently 51 fighting types in the world of Pokémon. 51 is a bit too much for a character lineup for a fighting game, so I'd assume, whoever is developing this game, would narrow the list of playables down to final evo forms. This leaves us with:
Primeape
Poliwrath
Machamp
Hitmonlee
Hitmonchan
Mewtwo (maybe Mewtwo X form)
Heracross
Hitmontop
Blaziken
Breloom
Hariyama
Medicham
Infernape
Lucario
Toxicroak
Gallade
Emboar
Conkeldurr
Sawk
Scrafty
Mienshao
Cobalion
Terrakion
Virizion
Keldeo (with ability to change Ordinary/Resolute forms)
Meloetta
Chesnaught
Pangoro
Hawlucha
Which leaves us with a roster of 29 fighting type Pokémon for a 3D Tekken-like fight game. I'm down for that. And that's a fairly reasonable roster of fighters, too. I suppose the developers could round out the roster at 30 by adding the comedy option character of Pikachu to the list, too.