The SP is balanced with the current acceleration, if they change it then they break the game, they make it too easy. Everyone has to have the same settings in MP for obvious reasons.
I dont see how it would break anything. The acceleration just makes it hard to aim, you could just have restricted maximum sensitivity speed to whatever GG wanted, end result would have been exactly the same pacing, but people who actually have played any fps besides PD:Z on consoles would instantly feel at home.
Depends on how KBM was patched in, I'd be ok with it. Having an alternate faster control system doesn't throw the balance off in MP since every player would be free to choose whatever suits them.
KBM would not work vs people with normal gamepads. KB+M is far to superior, they would have to go around and actively try and make the KB+M setup be bad. It would throw off the balance completely, because most people surely prefer to just play with a gamepad when they play on their consoles, while now, they would be forced to use KB+M if they wanted any chance of winning.
Aspecially if you let the KB+M to have higher sensitivity than the gamepads, as maximum sensitivity allways wins as long as you get used to the speed.
There is not a single implementation of KB+M vs gamepads in games that have shown otherwise. KB+M vs gamepad in UT3 means insta death if your the one holding a gamepad (atleast if your playing against somebody as good as you are.)
In shadowrun they had to give autoaiming and other implementations to the gamepads (and actively restrict KB+M) in order to try and level the playing field. KB+M wins everytime, there is not a single thing that a gamepad can do better when it comes to FPS games, atleast nothing that will alter the outcome of a game.