I wouldn't place too much faith in that "Build Sydney" blog you've linked to.
We at Build Sydney are dedicated to bringing you the latest developments and updates happening in the construction & infrastructure industry within the Sydney basin. The aim of Build Sydney News is to publish building & construction information to keep track of Sydney's developing transport, infrastructure, dwellings & ever-expanding built environment.
They aren't affiliated with any Government body, have not provided any links to reports, costings or routes, beyond the NSW Governments pie-in-the-sky wish-list about what "potential" routes there are. To do what they suggest would bankrupt the state of NSW, assuming it is even physically possible, which I doubt.
Take a look at their table of travel times. Sydney-Canberra (HS Rail >250kp/h) 1.0 Hour travel time.
The straight line distance
between the two is 250km, so you would have to average
250km/hr for the entire trip, and have a route distance not greater than 250km to achieve that. Any increase in track km's requires a consequent increase in required average speed. The Japanese have a maximum speed of 320km/hr on their lines, the Chinese, 350km/hr. The Chinese speed would make the claimed Sydney-Goulburn 30 minute time achievable if they got upto 350km on leaving Central and held that speed, in a straight line
all the way to Goulburn.
The Governments website is nothing more than some marketing muppet's wet dream and doesn't have the slightest idea about the difficulty involved running a railway over some of the most inhospitable terrain in the country for such an endeavour - bearing in mind by necessity it would have to be underground until leaving the suburban area as you aren't going to be able to compulsorily acquire several thousand homes to build their toy.