Add a full singleplayer sidescroller style beat em up mode to every fighting game and they will quadruple in sales.

Half the work is already done. Just make maybe 2 simplistic combatants meant for NPCs use other characters as boss fights.
The stages from the normal mode could easily be expanded into full levels with just a couple extra guys to lay out the assets as the rest of the game is worked on.

I am fucking tell you right now.
Hybridize fighting games to feature a brawler mode and watch the money flow.
Street Fighter accepted you need a good singleplayer experience and it was very successful. IF YOU DEVELOP A FIGHTING GAME PAY ATTENTION TO THAT. Even something basic as fuck like Tekken Force can radically boost sales from someone curious about something other than the same fucking thing like a Madden game.

FIGHTING GAMES NEED MORE FIGHTING MODES
NOT JUST A ROSTER AND A VERSUS MODE
IT'S WHY I DON'T BUY THEM