True, the equipment inside them can become difficult to support with time but over their life much of it,
The swedes LOTE their vastergotland class, commissioned 1989. Became sodermanland class, to be later sold to poland. Singapore still has the swedish archers.. So there is evidence the submarine design often has a long life. So Australia isn't alone in LOTE of these types of submarines.
IMO I just wishes for new engine/batteries. If we ever have a global conflict happen before our SSNs. I think we will regret not doing that. There is a big difference between managing the twilight years of an aging platform in peacetime, and high intensity combat operations with long transits, intense and long patrols. The engines would require huge work to do and be a tech dead end for Australia.
While its money, we are going to build SSNs here, and I think having a project with a bit more meat in it, requiring more active risk and more technical skill would prime the well more actively. Lessons learnt are going to be better to be learnt the hard way on an outgoing platform, rather than a ultra complex new platform that even moderate cost estimates put a 10 times the cost and perhaps complexity. Its one of the few times where I would support attempting a project even if risk of failure is significant.
Historical examples include the US Guppy program. The Swedes with the vastergoltand to sodermanland class (which included a hull extension). The US George washing SSBN program, with a 130ft extension, the Sturgeons.
Japan also fitted lithium batteries to the 11th of the soryus.. while a new build, it was basically a re-engineering of an existing design. for 1 boat. they have about 6+ years of operational experience across multiple boats now.
Batteries can be made to fit the same weight, size profile, but superior performance. So the engineering, while significant, isn't as risky and as massive as re-designing the entire boat for new engines/exhaust/generators. Enhancing submarine battery tech is relevant going forward for UUVs. Even if it was just used for hotel load, something that may apply to the new AUKUS subs anyway. Even if the first 2 subs were built without such features, and it was only included on the last batch.
But I assume such discussions are already being had and assessed.