Also newsworthy as the NSA is an organization with theoretically no commercial interest. So they're filing for a patent for what reason?

Aside from the grant money the idea of making additional cybernetics is a more difficult one. With prosthetic limbs the idea is to detect the neurological activity associated with executing a task one's nervous system is trained to do. For lack of a better term, the nervous systems base instruction set is insufficient to control limb it doesn't have.