Could Australia buy an interim AIP submarine?

Would an air-independent-propulsion replacement for Collins have been a useful interim step before nuclear submarines?

Not really; Australia's long-range requirement lacked an easy conventional match, and every option still faced major technology-transfer and industrial-capacity problems.

The Collins replacement had to combine very long range with non-nuclear propulsion, a difficult compromise that helped undermine the French programme. Japanese boats offered one possible conventional direction, but technology transfer and Australian construction capacity remained obstacles. Australia possessed uranium resources but lacked the domestic reactor and support system required for nuclear boats. There was no simple AIP interim solution, and building the required nuclear infrastructure would take time.