According to the patent other people in here have already linked, the feature of the gamepad will be that it uses "modules". Modules like directional pads, touch pads or trackballs. You will stick these modules into the pad and they will use interfaces within the controller.

Not sure just how sturdy the thing will be, all this talk about separate components being stuck together by the user sounds kinda fragile. But if it is, you will be able to configure your pad just the way you want.