Some comments- its unbelievable the two major and growing population centers on the route are served by spurs-Gold Coast/Ballina and Canberra. I suspect trip generation models in these sub-corridors need investigation
The short -term answer is the one suggested to be used for Homebush as the alternative Sydney Terminal, identify requirements, and reserve/protect both options as required.
Gold Coast - Ballina is particularly interesting, if there is No HSR a very similar corridor will be needed for extention of QR through northern NSW and I don't think chosen route will be through Murwullimbah. The argument that Casino route is shorter doesn't stand up, if compared with Gold Coast/Ballina/then direct coastal to Coffs Harbour (and people live on and are still moving to the coast).
Apart from these sections no doubt NIMBYs will start once they realise this has nothing to do with current railway and route reservation will occur in next ten years even if its construction doesn't start until 2060.
That raises an interesting Question. The suggestion has already been made that freeway projects in NSW incorporate new alignments for existing rail routes. Using this logic The Newcastle/Brisbane corridor would be reserved wide enough for HSR plus a double track "old style railway" sections of which might well be financially viable before HSR is built. I could easily of missed discussion of this.
What is missing is identification of other projects needed, Sydney and Melbourne Airport links for example and what happens to existing passenger services. can the XPT last to 2050/60?
It may never be built but personally I'd go for a twenty year delay, But as with Inland Freight route corridor reservation must start now.
A real public debate is needed and the sooner it starts the better.