As much as that demagoge is a chaos making machine (which I will suggest is what a good portion of the American population want in response to social inequality), he has been very direct about his military expecations of other countries. He has stated that if nations want American security then they need to pay for it. While the language around this may be somewhat vulgar and agressive, it would be one of the few principles of his that I would agree with.
In that regard I would suggest that Australia does pay its own way, with I think now at least 3% of GDP on the table for defence, more with the submarines. Moreover Australia has also made a significant move to buy American equipment (most of our Naval weapons and helos, army missiles, tanks and helos, and airforce planes for instance). We want to buy the submarines (at I suspect a premium) and part pay for their construction infrastructure. This all fits with his narrative. In some regards we represent a very lucrative cash cow, and that is something he also loves.
To be facetious (at least partially), I suspect if we agreed to name one of our subs after him we could comfortably clinch a deal.
From the strategic point of view, I agree with Brissy, in that transfer of SSNs will come with obligations (irrespective of what has otherwise been said). We will be expected to undertake the SSN patroling in our region, such that the USN can focus elsewhere. We will also be required to provide the USN access to our nuclear capable bases (east and west coast), be able to supply logistics (parts and maintenance) to their fleet, and provide them land for their purposes.
I doubt the Americans will ever depart FBW once they have mobilised in 2027, and will establish a permanent presence there (expect several hundred people to reside in Perth). Their ships and subs will remain home ported there for the long term, even after we have our own SSNs.
This commitment to duties and facilities will be the necessary underpinning for a US president to confirm the SSN capability has not been depleted. To state the obvious, we will become a copy of Guam or Okinawa for the American forces.
I don't think we will be asked to formally agree to support them in future combat, but that is something we have already agreed to with past behaviour.