Was that you at the very back of the train? I thought I saw the guard going back and forth.
The reason it run's non stop to Wycombe, is Chiltern use a Marylebone to High Wycombe ECS working to form the Paddington service.
IIRC the eventual plan is that Chiltern take over the Greenford branch service, but extend it to run from West Ealing to the bay at High Wycombe. The bay at Greenford will no longer be needed as it can only handle a short train, Chiltern will serve South Greenford station and then interchange with the central line at Ruislip. This will give Chiltern a direct interchange with Crossrail at West Ealing, Chiltern using platform 5 and a new platform 6 built on the old milk dock.