Crossrail will offer a small boost in terms of attractiveness for Drayton Green and Castle Bar Park passengers, but I can't ever see it getting any serious boost, given the Central Line at Greenford and Hanwell/West Ealing stations are not too far away. Back to a 30-minute frequency (eventually) is probably the best I can foresee.
I seem to remember a proposal for Crossrail to High Wycombe ... far more attractive for commuters for some of the 'burbs on that line headed to The City and Docklands than via Marylebone?
That was western corrideor B, of six considered. It was subjected to the government's NATA process, using the GOMMS criteria, but the result (before 2007, I think) was -
The Aylesbury Line (corridor B) performed strongly against the sub-objectives of transport economic efficiency and reliability, however, this corridor was not selected for inclusion in the preferred scheme. This reflects the very significant adverse contractual impacts that Crossrail would impose on the current Chiltern Line franchise and the Metronet (Sub-Surface Lines) Public-Private Partnership concession for the Metropolitan line.