Five integrated runways for a lot less than $70 Billion - all the right side of London
Oh God I despair.
Utterly commercially unappealing.
Scenario 1. Get off an aircraft at Schiphol, walk to gate, connect.
Scenario 2. Arrive at Upper Heyford. Get on a train. Hope your luggage makes it. Arrive LHR. get on another train to RAF Northolt. Pray your luggage makes it. connect.
Just because something is possible technically does not mean it is comercially attractive and competitive and it absolutely needs to be.