Its difficult for future Australian SSNs, with weapons grade HEU reactors, to escape accusations of nuclear Proliferation. But Australia WILL need nuclear weapons by the 2030s. (Cartoon via Voice of America's POLIGRAPH(dot)info)
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China's objections, voiced to the IAEA this week, are Inconvenient yet accurate.
China's power projection south gives Australia good cause to have nuclear weapons options.
Very rapid launch of Australian nuclear missiles would improve if Australia's 8 future SSNs had vertical launch systems. Thinking post astutely I would hope the Brits will design their own UK RN 2040s SSN(R)s with a Virginia Payload Module (VPM) with "two multipurpose Virginia Payload Tubes (VPT)". Each VPT might be capable of carrying 7 vertically launched Tomahawks or, better still, Hypersonic Cruise or small Ballistic missiles.
Any Australian SSN will certainly use the US Combat System (consisting of weapons, torpedo tubes, sensors, comms equipment and huge databases) that is already on the Collins. This would amount to about 33% of a RAN SSN(R). If the Brits didn't incorporate VPMs into their SSN(R)s then a RAN ONLY SSN(R) special fitout of a VPM (around 10% of a RAN SSN(R)) would cause many knock-on readjustments (5+%) and extrordinary added costs for a RAN SSN(R).
Australia buying-building a 50% (with knock-ons) US content RAN SSN(R) would be probably much more problem prone and expensive than a UK or US SSN of 2040s vintage. It would be much more logical for Australia to buy/build a US Virginia design - Block V or VI.
However, I see a PLAN B. ie: Australian SSBNs.
Alternatively Australia might consider building just 6 UK pattern SSN(R)s. Worldwide the top priority of SSNs are to defend ones navy's SSBNs (see "Main missions"here. Those 6 Australian SSNs could defend 4 Australian UK designed Dreadnought class SSBNs armed with Trident II (or Trident IIIs after 2040) ballistic missiles.
In the end Australia needs its own nuclear deterrent. After the Trump experience, and real chance of further US isolationism in future, Australia can no longer rely on a perhaps mythical US nuclear umbrella to protect us.
By 2030 the Australian public (who already seem to have been sufficiently scared/sensible about China - to accept Australian SSNs) might be sufficiently scared of a China gradually power projecting south, to consider Australian nuclear weapons a serious option.