The thing about wheel motor cars though is that they don't tend to turn well, you can't speed up a wheel motor electronically a whole lot more than max speed. I realize that BL motors can be run with different timing to modify speed, so perhaps that is what you'd have to do to achieve "proper" differential action with a wheel-motor car.
Currently there are some small brushless outrunners that can fit snugly in a Mini-Z wheel, and we (GSR) have toyed before with these kinds of motors in building a speed run car. For us, we only had to have two ESC's communicating with each other, and that's where we got stuck. If you want AWD you are going to have to deal with two more ESC's on top of that, and they each need to communicate with each other (L/R, F/B) for the car not to handle like crap.
This is a very tall order indeed, you get any headway with it it'll be quite a splash. Good luck.