Dave Arquati wrote:

Unfortunately the reason Greenford trains are being cut back
to West Ealing is that all line capacity on the Relief lines
is required for Crossrail services. Cutting back to West
Ealing will mean Greenford trains don't actually use the GW
at all other than for travelling to/from the depot.

This is why I suggested using the GW link line to run some of the
Crossrail trains to Greenford; unfortunately, the Central Line viaducts
would make it very difficult to get a link in from the bay platform to
the link line.