Australia is huge, but everyone lives in 7 cities (within a margin of error). A high speed rail that covered Melbourne/Albury/Canberra/Sydney/Newcastle/Tamworth?/Brisbane would have a huge impact.
The distances are (as the crow flies):
Melbourne-Albury: 260km
Albury-Canberra: 219km
Canberra-Sydney: 247km
Sydney-Newcastle: 117km
Newcastle-Tamworth: 219km
Tamworth-Brisbane: 450km
That last leg might need another break in it.
But at 300kph average speed that's 2.5 hours Melbourne - Sydney (CBD-CBD), say 3.5 hours with stopovers.
To get to Sydney for a 9:00 start in the CBD from Melbourne now takes (CBD - CBD):
Taxi: 30m + 1hr check in + 1.5 hour flight + 30m taxi: 3.5 hours.
I'd take the train any day. Space, able to work, sleep, dining car etc. Not affected by weather or other airport backlogs. You still get up at a god-awful time of the morning, but the actual travel would be much more tolerable.
Perth doesn't count as a major city? (% of that 30% live within its metro area. This isn't to say the 7-city grid is a bad idea, but your statement is inaccurate.
Perth (and Darwin) are essentally islands of their own.
Perth-Adelaide (nearest major metro) is 2,131km air mles, over the Great Austrailian Bight (ocean). Land route is 2,695 km (1,675 mi).
Darwin-Brisbane is even further: 2,848 km by air, 3,425 km by ground (2,128 mi).
By 300 kph HSR, those are 7+ hour trips, vs about 3 by air. And those are nearest-nighbour trips.
There is effectively no population between either location -- unless somehow induced (a possibility), a high-speed rail service would have tpo rely on endpoint-traffic only. Climate, economy, and ag productivity (low) make development unlikely.
By contrast, the southeastern zone of Adelaide-Melbourne-Canberra-Sydny-Brisbane, is compact with five major metros over 1,601 km (air), though the ground route is still 2,005 km (1,246 mi).
One more: later, trains will be faster. In the 20 years that I've been in Madrid time to my hometown has come down from 5.5 to little more than 4 hours.
Edit: last hour is not high speed because the rails are regular ones (the train adapts in a ten minutes stop) so the high speed interval went from 4.5 down to 3.
Last time when I checked, the 11km South West Rail Link in Sydney took 6 years to complete. 12 years after Kevin Rudd promised to build NBN for everyone, after billions of tax $ already spent, my places in inner west Sydney and inner south east Melbourne are still not connected to NBN.
If anyone asks me how long will it take to build the Melbourne to Sydney high speed rail, my honest answer would be 30-50 years.
The distances are (as the crow flies): Melbourne-Albury: 260km Albury-Canberra: 219km Canberra-Sydney: 247km Sydney-Newcastle: 117km Newcastle-Tamworth: 219km Tamworth-Brisbane: 450km
That last leg might need another break in it.
But at 300kph average speed that's 2.5 hours Melbourne - Sydney (CBD-CBD), say 3.5 hours with stopovers.
To get to Sydney for a 9:00 start in the CBD from Melbourne now takes (CBD - CBD): Taxi: 30m + 1hr check in + 1.5 hour flight + 30m taxi: 3.5 hours.
I'd take the train any day. Space, able to work, sleep, dining car etc. Not affected by weather or other airport backlogs. You still get up at a god-awful time of the morning, but the actual travel would be much more tolerable.