high speed rail a non-starter
High speed rail is expensive. Think around $40 per 100km in Japan, if you're a full-fare Shinkansen ticket holder (from memory). And that's in a country with a much higher population density than NSW & ACT. It would be more expensive in this country, even ignoring the need for a tunnel under the Blue Mountains.
It would also need stupendous cash up front from the public purse, which won't happen in NSW.
At the moment air travel is both cheaper and more convenient than rail for most people. No doubt that will change eventually...