I predict that the 'issue', to the Australian taxpayer, will be one of spiralling costs. To pose any credible counterthreat to this mythical Chinese invasion, Australia would need a sub base in the N/NE of this rather large country- also to act as a base for 'visiting' US boats. Otherwise, it's a bit like the sub base in San Diego being the depot for subs patrolling the Nth Atlantic.
Furthermore, since the decision was made to eschew nuclear energy & research in the mid 70's, Australia has no qualified nuclear technicians etc at all. Everything, including people, will need to be imported. It's a considerable challenge. Then again, it still makes more sense than proceeding with the baguettes.