I really wish we had high speed rail in Australia. I'd pick a 600km/h train over a plane any day.
This would make sense along coasts though but you wouldn't be able to cross the country from sea to sea in a few hours of course.
What's good with trains is that you can hop in at the very last moment (when the bell rings, happened to me a couple times) and the train stops in the center of cities, instead of the suburbs. This is the main reason why high speed train in France can compete with airplanes when crossing the country. By plane I must first reach the airport (30 mins), have some time ahead before embarking (30 mins), the flight is 1 hour long but the time to actually take off and pick back your luggages it's almost 2 hours long, and then you have to reach the center of your destination city (30 mins). By my generous estimates, it takes 3h30 to travel by plane North/South in France vs 4 hours by train.
And because currently not every railroad segment can support high speed trains going at full velocity (but work is in progress) it could take 3 hours. 300 km/h
Also note that Amdahl's law [1] applies in this context (there are diminishing returns in optimizing the speed of only one segment of the full path) and travelling the last kilometers accounts for a significant portion of the travel time.
For instance the TGV has to slow down when entering cities (because of the noise) and at some point in the development of the high speed rail network, it might become more interesting to dig long tunnels under cities for these trains rather than increasing the train's maximum speed.