No reason for gorilla-arm when touch is an alternative interaction mode and not a required one. You still have trackpad and keyboard. You can dynamically switch modes depending on the action.

Gorilla-arm was a fear based on the naive idea that if you had touch, you would be required to only use touch for every action.

Is apple going to be so restrained to keep the design of the OS as a mouse first experience or are they going to cripple information density so I might be able to close a window with my elbow?