The best way to achieve that would be to make Old Oak Common a two tier station. The Wycombe Line begins climbing at Wells House Road and veers north to reach OOC High Level and then proceeds to drop down into South West Sidings to connect with both the North London Line (and Willesden Junction) and the South West Line (and the West London Line)
This would achieve your objective, give far more point to the projected Chiltern service to OOC and make that big hub even more useful to even more people.
Not sure about Chiltern <> West London Line until you then have a good look at a few other bits and pieces.
You have to weigh up the number of trains operating on each line. Then, any predicted growth and push that all together into a neat bundle.
For example:
- Willesden Junction <> Stratford every 5 minutes
- Willesden Junction <> Richmond every 10-15 minutes
- Clapham Junction <> Willesden / Old Oak approx. every 5 minutes
- Willesden / Old Oak <> Kew Bridge every 15 minutes
- Willesden / Old Oak <> Cricklewood / West Hampstead every 15 minutes
- Willesden / Old Oak <> Watford (via WCML) every 30 minutes
So even if you manage Richmond <> Stratford every 10 minutes and Clapham Junction <> Stratford every 10 minutes, that leaves a 10-minutely path from Clapham. Half-hourly on that would be Watford Junction / Milton Keynes; so this would mean terminating the other 4tph (10-20-10-20) in the 'Low Level' platforms underneath Willesden Junction. New platforms, therefore. You could alternatively divert some to Wembley Central via the Sudbury diveunder and build a platform near the Loco Holding Siding / next to Platform 6.
Kew Bridge is picked instead of Hounslow so that peak capacity is provided on the Hounslow Loop for Waterloo traffic; and that would be to Brent Cross as West Hampstead would be easily accessible from Willesden / Old Oak interchange on the existing NLL. It would be around every 15 minutes but probably slightly biased one way or the other to accommodate the 10-minutely Richmond.
That leaves the Chiltern option. Realistically the best thing would be to convert Greenford <> West Ealing into some sort of Tram option, down Manor Road into West Ealing then along Uxbridge Road to Ealing Broadway. Some trams from Greenford, some from Southall. At the east end, past Ealing Common with some to Shepherds Bush and some to Acton Main Line / Old Oak.