Id want to see same train service from the Illawarra/Cronulla to Parramatta (and possibly beyond). Given alignments and tunnels im not sure how we would get this service to go through Hurstville. But its not impossible.
Their alignment looks to go Kogarah, Kingsgrove, Roselands, Bankstown, Villawood, Guildford, Granville, Parramatta. Not sure if using the Bankstown-Lidcombe section of track might be a cheaper option? Though doesn't connect the Villawood-Granville areas (not sure if they're worth connecting or not TBH but it could be a capacity issue on Lidcombe-Parramatta too). Also not sure if Metro is going to use Bankstown-Regents Park section or not either, time will tell.
Connecting to Strathfield then Parramatta might be a better idea too - allows northern connections too which in itself would take more journeys out of Central that may not need to go that way. That might be part of a case for another north-south corridor though.
screw this same train crap. Changing trains is perfectly acceptable and you need to forget about having trains go everywhere from everywhere. That isn't possible or efficient. You can forget about using the existing ST network as well as if this option goes ahead it will be a north south metro connecting a whole stack of lines and areas.
Georges river councils alignment is what is beneficial for Kogarah and not what is beneficial for Sydney. The line going directly north at Olympic park metro with a change for metro west not only makes 30 minutes to Parramatta possible but also further north to macquarrie uni as well. This is much more beneficial for Sydney then running yet another train line to Parramatta.