I've also wondered about towing, but in a different way. Many times at larger airports, long-haul aircraft are kept in the airline's hangar until they are needed at the gate. They are then towed (or rarely, taxied) from the hangar to the gate before they are opened for passenger boarding. And possibly after the passengers have deboarded and the luggage taken off, the empty aircraft could be taxied automatically from the gate to the hangar. Most AFCADs contain the necessary information to move between the hangar and the gate, but I don't know how difficult it would be to add these functions. Just an idea.