From 1990 to 1996 i was the Business and Operations Manager for the NSE part of Crossrail (1) , and an enjoyable job it was. Shame the Tories canned it.
It came from the 1989 Central London Rail study but there were thin ideas before that. The surface section was planned to have - on the west - 12 tph each off the Reading and Aylesbury branches ,but later amended as work was done to a 14 / 10 mix as there was "too much service" for the Met and Chiltern corridor.
The Met would have had 4 (peak) "fast" Aylesbury , 4 semi/fast Amersham and 2 tph (all day) from Chesham. The route would have accessed Neasden South Junction via a link from Old Oak Common and a touch of the Dudden Hill line , taking over the diesel route to Harrow North Junction and then on to Moor Park etc. The "Met Main" would have ended up as an Uxbridge and Watford Met service only (there were hopes of somehow doing Watford Junction) - the Crossrail trains would have been segregated entirely from the Met residuals , - a bit of a challenge as the formation was a bit tight.
No interface at all with the Jubilee line , apart from Crossrail platforms at Wembley Park.
(The Reading line would have been 4 Reading semi/fast , 2 Maidenhead , 4 Slough and 2 Hayes and 2 West Ealing. Heathrow was sort of considered but a bit of a debate there. (as HEX was about to be burst into life)
Only when pressure on the core scheme came up , was an (unofficial) look made at the Chiltern main route towards Wycombe and a not bad idea IMHO , to connect into the WCML slow via a clever tunnel under Kensal Green cemetary to surface at the Willesden TMD to join the WCML slows for a Tring and Milton Keynes service of no more than 8 tph. We , the plotters called this "Greater Crossrail" - we had other ideas for the East involving Southend Victoria and the LT&S.
It was "broadly" feasible and would have brought in more benefits , but frankly not allowed to develop it formally , as it might have affected the core scheme. Which turned out to be doomed........