Handicapped to make it roughly equal...
Certainly in traditional FPS games, it's not sustainable to have some playing with gamepads, and some with mouse and keyboard. It's been tried and doesn't work. A while back I had been playing Crysis 2 with a gamepad, thoughtlessly went into multiplayer with it, and died over and over again without a single kill. When I twigged, I switched to mouse and keyboard, still died a lot, but got several kills to my name and actually felt like I could vaguely compete.
Unless the two control systems are roughly balanced, there'll more than likely be one dominant control system in the 'all' group. Given how many people are excited about playing this game with a stick, it would be sad if they went online, got sniped by a precision mouser from 2km, and had to put their X52 pro in the cupboard to collect dust, while we all point-and-click from a distance.
Heh. My brother became a console gamer and swore blind that controller was better than keyboard and mouse for FPS. That all changed the day we played COD2 on the PC, he on his XBOX controller and all other players using K/M.