Yeah well, up front cost scares many who want to see a profit before construction begins.
Let's just look at the land requirements. All the train stations & tracks in place now take up an enormous amount of land.
Imagine the rail running overhead, leaving so much land for much needed AND profitable parking space.
It'd have to be a 30 or so year project to gradually morph with the existing system but gradually taking the old system out.
A project like this requires vision & patience not be cast aside by instant gratification & no plans for the future.
Employment opportunities, reduced environmental impact etc would be the eventual outcome.
Alas, so many are just so hung up on maintaining status quo, especially the progressives !
They can't see what manufacturing for such & building such a project would do to the Australian economy & society. Maybe it's because too many would benefit instead of just the normal few ?

Sylvia our metropolitan rail systems are basically a means to deliver workers to a central point, the inner city. As inner city workers are in general the highest paid workers in the country, I can see no reason the lower paid workers, generally required to provide their own transport to workplaces not serviced by the rail network, or even a public bus service, should have to subsidies the transport of the more wealthy workers.

In consideration of this I believe all tax payer funded transport should be full cost recovery, & can see no way subsidised public transport is equable.

I doubt that the Very Fast Train as per France will ever be achieved in
Australia. The country is too big to make it economic.
Small countries like France and Germany can just afford it.
The fares could never be as low as air fares.
What we need is the fast enough train.
The tracks were laid in the 19th century using horses and scoops.
The track could be relayed say between Campbelltown and Goulburn as a
first step. This would take, at a guess an hour of the time to Goulburn.
There is a hidden advantage in that freight would be a lot
faster and would not have to be hived off into the middle of the night
as it is now. So more on time freight and faster passenger carriage.
It would need track relaying to higher standards as per the UK.
I do not see tilt trains being an answer, more customer comfort, sure,
but the centrifugal forces are just the same and limit speed.
NSW Rail has conducted 200 Km/hr trials using the XPTs south of Wagga
quite successfully, but they had to put guards on every level crossing.

I can't see it happening when we cannot guarantee electricity.

I have no doubt we will get fast trains in the bush
They may even come because of the costs of other forms of transport and the infrastructure they need
Just because we do not use them does not say others will not freight alone holds promise for cost effective fast trains

The situation could change dramatically if aviation fuel becomes tight
in supply. There is no immediate likelihood of that in the near future
but as the tight oil in the US declines further then demand will shift.
Look ahead 10 years and there will be changes of that nature.

Of course the greenies could get control of the government and any
transport would be under threat.
Big money needed whichever way we go.

Bazz, trains become uncomfortable on curves at speeds much lower then the speeds at which there's any danger of the train coming off the track. Tilt trains exploit this by making the higher speeds comfortable. It does mean that the safety margins are reduced, so tilt trains need protection against excess speed.

Level crossings are a hazard at higher speeds, which is presumably why guards were used during tests. But the risks can be addressed, so level crossings should not be seen as a permanent obstacle.

The NSW part of the route south from Sydney towards Melbourne is particularly bad when it comes to tight curves, and on tight curves, tilt trains don't provide so much benefit. It would involve some expense to improve that route.