Well it has been done on concept cars bit it would be a bit wierd for those of us used to driving with conventional controls.
YOu don't need a carPC to do it. A lot of cars now are drive-by wire so you can just use any method of controling the systems you want.
While cars still have a mechanical linkage between the steering wheel it is easy to do away with it on these modern cars with electric power steering. I have seen something like this done on speed sensitive steering that actually changes the angle the wheels turn in relation to the wheel in response to speed. A step further from those cars that weight up the steering at speed.
But a few cars now have fully electronic throttle control as it makes things like cruise control easier to do and you dont have to worry about cables snapping. Most cars from the mid 90's on have stepper motors to control the idle so its not really anything new.