My two cents on the topic is that HSR from Melbourne to Sydney should implemented as a series of incremental upgrades, rather than a single megaproject.
It wasn't done as single megaproject. Instead, it was done in small segments. A bypass around a town. A section of road between two town upgraded to dual carriageway. Eventually, over 40 years, the whole road was upgraded.
We should be doing the same thing with the train line from Melbourne to Sydney.