Don't rain on their parade, it will never happen! What would one of these gadgets cost? not a little. How many fancy pilot operated tugs would you
need to line up all the jets on the taxiway at Kennedy? And then once detached from the aircraft, you would have to construct an extra taxiway for the tug to get back for the next customer.
The only sillier idea I've ever seen are those extremely peculiar busses that somebody sold to the airport design committee at Washington Dulles....you know, the ones that go up and down and cross the active taxiways?