Surely there is a really easy way of thinking about this?
The Central line will need new stock.
There is a need to continue to supply a form of freight infrastructure along the Greenford branch to get to Park Royal and on the way to the Chilterns.
Arguably, if you use the Bakerloo line as a template, you have the opportunity to run freight over Network Rail infrastructure? Doesn't the RHTT run across the likes of the Bakerloo line, ergo proving locos and wagons will go over 4th rail?
Therefore, surely, if you assume there are reasonable gaps in the timetable, there would be capacity for services on the West End of the Central line from the likes of West Ruislip towards both West Ealing and Greenford?
Indeed, you might suggest in favour of rebuilding South Ruislip as a facility for a half-hourly Chiltern Metro service to be looped in both directions, and then convert West Ruislip into a nicely-wide island for Chiltern services (aka just two platform through lines, not the existing three-track layout) with some goods loops installed just north of West Ruislip for both directions? That way you can effectively run and regulate a freight service.
Then I would potentially have to suggest that if the Central line runs a frequency of something like 34tph during high peak, of which there is about 10tph on the Ealing Broadway branch, there is surely some space for a West Ruislip to Old Oak Common shuttle with a little bit of remodelling around North Acton, even if it only enables something like 4tph at high peak, as people will then make the effort to jump on that specific service.
Then, if we now assume a standardised signalling system with new trains, time to finally reconnect the Uxbridge branch and therefore offer an Uxbridge to West Ealing service at a rate of 4tph, again with minor remodelling in the Greenford area.
Therefore you end up with a better Central line, and a new suite of services and journeys in West London, notably Uxbridge to West Ealing, West Ruislip to Old Oak Common and then the existing sorts of services.