Congress is desperate to get Virginia class production up from 2 a year to 3 just to meet their own needs - not sure they could fit in any orders for Australia.
Regardless production is due to end in 2032-33 with the ramp up of SSNX production.
With the timescales being discussed I would suggest SSNX would be the more likely candidate - and it seems better fitted to Australian needs.
The current shortfall in numbers of fleet SSNs, and projected fleet shrinkage, would see to limit the chances of any loaners - though establishing a permanent detachment to a home port in Adelaide might be a way forward
.
https://news.usni.org/2020/11/18/nav...pyard-capacity
https://www.navalnews.com/naval-news...-ssnx-program/
https://news.usni.org/2021/08/11/rep...ck-submarine-3