The sharing is better than nothing. For the first/last mile of accessing central stations, that is the norm in countries like Germany, and a Sydney-Melbourne Shinkansen turning into a XPT somewhere around Wagga Wagga where it rejoins the legacy line is also doable, and better than the status quo. And gauge seems to be a settled issue everywhere except for Queensland north of Brisbane and the Victorian suburban/regional networks, whose interstate-reaching routes have all been regauged.
Trickier details would be electrification (you’d want 25kV AC to deliver enough power to accelerate fast, but in Melbourne/Sydney, you may need to either make do with lower legacy voltages, necessitating multi-system capabilities as in Europe, or have a dedicated road).
The sharing is better than nothing. For the first/last mile of accessing central stations, that is the norm in countries like Germany, and a Sydney-Melbourne Shinkansen turning into a XPT somewhere around Wagga Wagga where it rejoins the legacy line is also doable, and better than the status quo. And gauge seems to be a settled issue everywhere except for Queensland north of Brisbane and the Victorian suburban/regional networks, whose interstate-reaching routes have all been regauged.
Trickier details would be electrification (you’d want 25kV AC to deliver enough power to accelerate fast, but in Melbourne/Sydney, you may need to either make do with lower legacy voltages, necessitating multi-system capabilities as in Europe, or have a dedicated road).