Australia should take example from countries having high-speed railways. Being Japan, China, or any Europaen countries. (gues, I'm in Europe ;) ) The US is a bad example. Sure you have large distance as in the US, but expertise is not there. There is only one highspeed line between Boston and New York city, if I'm correct).

High speed train need its own track, it's too fast at 300+ kmh, it needs protections from and for wild life around it, an onboard signaling system. All you don't need below 200kmh.

Contrary to the article, when a highspeed train uses normal tracks, it has to go slow (200kmh max), and use visual signals. It becomes a classic train. So there are expenses to be made building tracks for highspeed trains. It's not cheap.

Privatizing rails, taking examples from the UK and Paris - Bordeaux in France is a baaaaaaaad move. I think the UK rebought its first rail company. Paris - Bordeaux highspeed track is private and the french national operator SNCF must run its trains, even empty, to use it per contract. And seat prices are quite high compared to other (public) lines in France.

However as I see here in Switzerland, privatizaton can happen if well done. Switzerland has about 100 private rail, boat and coaches companies across the country... for 8 millions people, and one ticket and one timetable for everything. This is very centralized around the main train operator (which is a private company, 80% owned by the confederation).