The devil you know…

No one would ever trust China, not Vietnam, not anyone unwilling to take orders from them. The terms would be heavy.

Like all things it depends on the terms, in my mind though China would probably be incentivized to give us a good deal - Im sure they would be very amused delivering real hardware while the USA continues to demonstrate their incompetence at shipbuilding. It would also signal that Australia wants to sit out any USA/China war, which might be hard to do politically (which is maybe why Im not PM) but its certainly the position I hope Aus ends up taking should these 2 buffoons start a real blue

Why? They can buy subs from France who was the other option when Australia was last shopping around.

Let’s switch suppliers a second time?

We need to pay the money to USA as tribute so its a write-off anyway, but I have low confidence we will ever see working hardware from it. However I bet China would actually prioritise delivery of some new subs if we pivoted to using them as our naval supplier, to win mindshare in the west as an alternative to America or Russia as an arms supplier. and we set up the next 100 years of paying off bigger countries to leave us alone, which honestly worked well enough the last 100 years

Eh. They aren't meant to be delivered for at least 5 years by which point US politics will have swung the other direction again.