The Airport line line should never have used the current surface plats at Central, certainly 22/23 is not fit for purpose (multiple personal experience) for use as a station for airport trains. If at all possible it should have used the unused platforms.
In principle I totally agree that St James spare platforms should have been used for terminating anything, most likely T9 as the demand on others ie Bankstown and Airport as their demand is higher and will grow faster than T9. But the more I discuss this with people in construction the more the simple answer No, No NFW as this opens up numerous issues with modern engineering design and construction interacting with 100 year old abandoned part completed works. One Mining guy told me he was surprised the abandoned tunnels were simply not filled with concrete, which is what would be required today.
Airport line, which is basically city to eventually East Hills will be a very busy corridor within a decade or so and will be stand alone with no other services using the tracks. Macuthur will only take the extra pair of tracks from East Hills then express via Sydenham.
The City Circle would have needed relief from some of its current services. So eventually there will be 20 trains per hour coming off the Inner West tracks and southern track feeder
From West, Inner West and Liverpool services
From South, Macuthur and East Hills via Airport
So Bankstown or something had to go and Bankstown was the obvious choice as it was and is stand alone. Liverpool easily managed and may eventually likely be Metro anyway.
Regarding the platform lengths on Bankstown line.
Yes its not surprising when you look at the Bankstown line on Sat view the issues raised. I think this is why the origianal plan was a long shut down, basically so the entire platforms could be cut back and track completely realigned. But with the opposition to long shut, this is outcome. I suspect in future they will still do it, but that issue is for the distance future when the frequency is maxed out and the permanent fix is required and the line converted to 8 car length again.
On a similar topic to why for some of the rail projects are being done around Sydney the way they are, spoke with a friend last night who used to live in a house backing close to Asquith station, they along with all their neighbours (all on uncondensed blocks, ie Qtr ac) were basically forced out about 10 + years ago (they were last to sell and her son now lives in a townhouse situated over where their pool used to be). What the govt did/is still doing to accomdate the growth in Sydney is that any land near a railway station that gets flagged for redevelopment to higher density gets "incentives" from the govt. So the govt flagged locations as prime for redevelopment based on railway spare capacity and how much of the local housing was still the traditional Qtr acre blocks, older houses etc. Basically looking at land based on number of bodies per m2 and starting with the lowest number next to railway corridors with easy growth options. My friend is in a govt job that gives her access to security, strategy etc and helps to shape policy that is bi-partisan so she can see what is happening from both sides of the fence.
Anyway, basically we discussed the Bankstown line corridor. Her comments, she said anyone who thinks a dozen or so trains an hr on that corridor will cut in within next 10 - 20 years is dreaming. She said people down that way including the local Mayor need to accept that this corridor within a decade of the Metro opening will start looking more like the lower NSL high rises than low density suburbia. She also said the line will no doubt reach Liverpool within a decade or so of opening as this will be required to access the route to Paramatta and its future CBD.
She said look at the Paramatta Metro station precint, they didn't need to do that for just add the station. There is also a very good reason why the Paramatta Metro station is not next to the HR line, its Paramatta CBD starting to become more like Sydney with multiple station options. Those old run down low rise properties will be replaced with modern, denser, taller office and some resisdential towers. This is the start of the growth boom and the private sector wants the infrastruture in place to justify investment.