Neither did Japan until the Shinkansen. (In fact, aren’t both Cape-gauge?)

Any interstate HSR link to Brisbane would be standard gauge, as the XPT is. An intrastate link going north towards Cairns/Townsville may be classic-compatible Cape gauge if done incrementally, though given that one would typically break one’s journey in Brisbane, this is not catastrophic. Unless suddenly funds become available to build a new Shinkansen-style network from scratch, in which case standard-gauge would be the way to go.