I would presume that on opening of a Western Express (WEX a.k.a. CBD enhancement project), the Blue Mountains trains would use it along with the Western Line trains.
Harbour Bridge trains (sector 3):
4/hour Hornsby all to Eastwood, West Ryde, Strathfield, Redfern
4/hour Cabramatta via Granville
4/hour Glenfield via Regents Park
Moving the South Line to the Harbour Bridge has to be considered a given as it is a faster path on the middle pair of tracks (suburbans) from Strathfield to Macdonaldtown and no conflicting move penalty for doing so as applied in the past with that option.
The above assumes that turnbacks would be constructed at Regents Park (to turn around Bankstown trains) and at Cabramatta, with the Lidcombe turnback becoming unneeded.
A Glenfield via Regents Park to the Harbour Bridge should be somewhat faster than the existing service to Liverpool and help get people out of their cars. The major limitation with the proposed patterns is that there is little room to allow for growth in patronage on the Western Line, other than with the larger trains proposed, without kicking the Blue Mountains trains out onto the Harbour Bridge, which in turn blocks increases in the Harbour Bridge services. One solution might be a Homebush-Lidcombe sextuplication, but I have no idea what that would cost.
Outer City Circle, AM peak, would handle all trains from Bankstown, Ashfield, Homebush and Campbelltown via Sydenham. This would enable simplicity in timetabling and therefore reliability as every train past Erskenville platform 1 would head the same way, however it might be a little controversial as the via Museum path is left with significant unused capacity. The Erskenville-Sydenham sextuplication would be the next enhancement to increase capacity in this part of the network.
In the PM peak, I would expect that the Campbelltown via Sydenham trains would leave the CBD via Museum, however, the Bankstown trains would be more balanced running via Town Hall at all times.
You can see that the WEX would indeed be well used and the only thing preventing CBD capacity from the west from being fully populated is the lack of rolling stock. While the via Museum leg of the City Circle remains under utilised, that is left in reserve to allow for increased running via Revesby and Bankstown. This leg cannot be used for Western Line trains in any event and only 4 trains per hour in the AM peak from the Bankstown line are able to be moved to it and filled in by other trains from the West.
The justification for the North West Rail Link, contains a couple of interesting points in objective 4 in section 22.3.1:
(a) 29 million trips within 5 years of its opening, which is about half the number of trips currently using the bus system in the relevant region, region 4. Obviously, people will still continue to use buses into Parramatta and other locations but I expect more than half of bus users are going to or from the CBD-Macquarie Park area.
(b) almost 160 buses are to be removed from the CBD in the morning peak. This is approximately the amount of buses which enter the CBD in the morning peak from the North West.
I have little doubt that point (b) would not actually happen within the next decade, particularly while the rail-rail interchange at Chatswood remains.
Basically, the justification does not suggest an increase in the public transport usage in the North West.