I don't think we can say with any certainty yet how the post CBD metro will affect operations on other lines, particularly T1 and T9, although from reports so far the intention is to use the freed up paths through the City Circle for increased T8 services via both Sydenham and the Airport Line. There's also the option of diverting the T9 Epping services in the peak, to the City Circle Outer via Town Hall, merging with T2 at the flying junctions and all T8 services using the City Circle Inner via Museum.
On the face of it, your suggestion for all T9 services including Intercity to run via the Mains from Strathfield into Sydney Terminal seems logical, but whether it is achievable politically is another matter.
It's not my suggestion, it's my reading of the tea leaves. Why else would they even have created the T9 brand? It's inconsistent with else they've done in terms of naming lines.
The trend has been "metro" style operation - the evidence for it is the way T2 currently operates. They expect to run high frequency services with simple stopping patterns, and travel times be buggered.
I think the original intention was for Cabramatta to Bankstown only be operated by feeder services to the Metro (needed to generate the patronage to justify it), but a few articles in the press about stations losing direct access to the CBD have squashed that.
The 8 extra slots freed up by the metro replacing T3 I have no doubt were intended to go to T8, but now 4 will likely go to T2 to provide 4tph all stations Liverpool to CBD via Regents Park.
Edit: Another reason to isolate T9 into Central Terminal is it allows that line to be franchised.
With respect djf, I think it's a bit of a stretch to suggest that the Northern Line was redesignated as T9 for the purpose of eventually diverting all of those services to Sydney Terminal. It's perfectly logical to differentiate this service from T1, although it shares the same tracks from Strathfield to the CBD and the North Shore Line. T1 is from Emu Plains to Berowra and T9 from Hornsby to Gordon. The fact that the T9 semi-express services are diverted from Hornsby to and from Sydney Terminal in the peak is merely because they can no longer operate via the ECRL, which has been converted to metro, and there are no slots available for them on the Suburban tracks from Strathfield to the CBD and across the Harbour Bridge to the North Shore Line. This is one of the unfortunate compromises which resulted from the ECRL being eliminated from the Sydney Trains network. In the off-peak, all T9 services operate through the CBD across the Harbour Bridge. It's also a bit far fetched to suggest that T9 is being prepared for franchising, as it shares tracks with CCN Intercity and freight and is totally impracticable. There are other lines such as T4 from Hurstville to Bondi Junction which could more readily be franchised, but I don't agree with that either, as it would still have to share tracks from Wolli Creek to Bondi Junction for Cronulla and Waterfall services.
I agree that the initial Liverpool to Bankstown T3 shuttle services were a contributing factor to justify patronage on the metro. However, taking sims at his word, if few actually use the existing T3 service from Liverpool to the CBD via Bankstown, then it is less likely they will use it in having to interchange to the metro. This is reinforced by the unexpected proposed preference of TfNSW for the restoration of the Liverpool via Regents Park services instead of the Liverpool to Bankstown shuttle, which seems to be at odds with their metro strategy. Perhaps from further investigation, they have eventually realised that the expectation of more interchange to the metro at Bankstown has been overestimated.
Just BTW, the T3 Bankstown Line currently has a frequency of 10tph into the City Circle, with 6tph via Town Hall and 4tph via Museum. There are still 2 spare slots via Museum, so when the Bankstown Line is converted to metro, there will be a total of 12 extra slots available.
The frequency and stopping patterns with the restoration of the Liverpool via Regents Park services still have to be determined, assuming the preferred Option 2 is adopted. It could involve replacement of the T2 Parramatta terminators with the Regents Park services and other adjustments to T1 Western Line services between Parramatta and Strathfield. We will just have to wait and see.