Also, how much does it decrease the fuel economy of the towing plane?
I sure wouldn't want to be on a Boeing 7XX flight with one of these things in tow. Just imagine the possibility for human and machine error, the plane in tow could cause all manner of issues for the leader.
Ever tried riding a bike and towing someone on another bike or a skateboard? It's perilous. Now do it in the air. Gutsy.