Could the US base a submarine or submarines out of Perth? Yes. It has happened before (WWII), they have submarine bases in Bahrain and Naples, and Perth is ~15,000 km from Hawaii, so even for a Nuclear submarine, that is a long way, and the Indian ocean is the hardest ocean for the US to project power into. Being able to rearm, refuel and having crews based out of Perth seems completely reasonable. Having a nuclear sub would be fantastic for Strait closure. They get regular visits,
au.usembassy.gov
The US and UK both seem interested in Australia having nuclear submarine construction, repair and sustainment capabilities. There is basically zero margin for expansion anywhere, and an accident or fire could severely impact build and sustainment capability. The US also already has a backlog of work. A base located between Indian and Pacific oceans would be useful long term anyway. In a war type scenario, routine maintenance, damage repair would significant upset the new build program.
I don't believe anyone else is going to build modules for US subs, not Australia, not anyone that isn't American, that is not going to happen for a whole bunch of reasons. So that undermines everything else in the story. He might as well said the Thor of the Asgardians and Alf from Melnac would personally work together to build subs for the Americans, its that jarring.
But Australia and UK could certainly have some work share, between them. But I don't expect this to be the bread and butter of the deal. The reactor is likely to come from the Americans, because the Americans have the fuel and the tech, its not certain, but its most likely. Again the US doesn't really want to mess up their yards with other countries build needs. But Australia could be called on to do some inspection and scrape and a lick of paint, freeing up their yards to more intensive work. They can't outsource sub work to other yards internationally, because of obvious reasons. With high tempo, platforms get warn out, with increasing tensions, missions become more daring and risky. So as speculation you could see how that would hang together.
So some basic ideas, combined with crazy, combined with Marcus Hellyer claiming everything is too expensive. In other words, nothing of substance.
Really we just have to wait this one out. We will be told next year.