How exactly would a traditional brawler work on a touchscreen?
Mobile games that have virtual pads and buttons on the screen are usually terrible.
A touch screen is a different medium, games have to be designed with its advantages and limitations in mind, by necessity, it changes the rules of play completely.
For a good adaptation from mouse/key to touchscreen, look at the Doom3 spinoff game for iPhone.
Brawlers are twitch games. You need immediate, reliable control over your character.
Arguably, you could get a clamshell joypad/button attachment for a mobile and thus turn it into a Gameboy/PSP style device... or you could just buy a DS or PSP and run OpenBOR on that.
Maybe you just don't want to look for your Final Fight and your Contact List in two different places?
A RPG with turn-based combat which reused 2D assets could be cool, you could make it play on a grid like Fallout and spend points on movement, regular attacks and charging special attacks. I would play that!