When I was typing my first post on the topic, I was called away, so only posted part of the full picture.
Two more problem areas arise.
1 The obvious one of the extra tugs needed. Tugs only travel short distances on the ramp. Some holding points would entail round trips of 3 or 4 miles, which takes time. Depending on the airport, it has been calculated that, to cater for peaks, up to 75% more tugs may be needed, but these may be idle for up to 18 hours per day.
2. Many environmentally sensitive airports now ban the use of the APU on the gate (and some for starting).
They provide hook ups for pre-conditioned air, electrics and pressurised air for starts.
Whilst the pressurised air could be deleted at the gate, the runway end start point would need all three, the gate the other two. Also, how would airconditioning and systems electrics be provided during the tow where APUs are banned?
There have been some innovative airport designs toted around in recent years. On has gates at either ends of parallel runways with arrivals one end, departures the other with a central service module for check in, customs, shopping etc., connected by a tram or subway. The gates would change us as the runways changed with the wind and there would be only the minimum safe distance from the gates to the runways.
Aircraft would be towed "dead" between arrival and departure gates.
A much more radical design has aircraft parked at remote stands close to the runway with no gates as such but the aircraft serviced by giant mobile lounges from a central service area. Does that seems similar to something they have been using in Virginia somewhere for over quarter of a century?