US seems to want increased submarine build and maintenance capacity. Australian boats would assist in this - more craftsmen, more facilities, more subcontractor capacity.
This capability is being added for Columbia, and Australian Virginia boats would decrease risk of this capital investment.
It seems likely that Virginia blocks will be in production until Columbia production matures.
Adding a boat every five years to Virginia production, while Columbus production spins up, would be difficult but not impossible. Mature Virginia production is the best value Australia could expect. It is a unique opportunity to negotiate price, training of Australian yard workers, supervision and support of maintenance facilities, long term maintenance contracts, decommissioning risk elimination, etc...