so keen to trash what could be quite a good idea?
It's a stupid idea in that it is trying to solve a problem that does not exist. We are not all that short of capacity in getting people into London. The core issue is one of making the hub and spoke work the best we can.
Lufthansa, KLM and to a lesser extent Air France have effective hub connectivity up against LHR. Using Northolt and mucking about with magic/special sterile and sealed buses between airfields fails on the key question of keeping the product competitve against the competition.
Have a look on flyertalk. Joe Public gets into a hysterical strop when the connection lacks an airbridge direct to the F'Lounge and the connecting aircraft ideally parked on the next stand. We need to get as close to that ideal as possible(!)
Perhaps you should start thinking outside the box
That's a lazy expression. Sometimes it's genius to do so, however much of the time, it's just whizzing off on a tangent.