With high vaccination rates in NSW and VIC if a few people find a way around the system that should not be a big issue. If the hospitals are not overwhelmed, then there should be no reason to restrict the movement of vaccinated people travelling internationally any more than happened pre-COVID.On a more practical note, I would imagine the bigger concern is how are you going to check the authenticity of the vaccine, good luck trying to get a common standard for vaccine certificate going globally anytime soon.
You can bet people will look for ways around vaccination requirement once they figure out which country has the weakest link in terms of vaccination certificate. Unlike a passport, you don't need to be a citizen of that country to be vaccinated.
Foreigners that travel here with a fraudulent vaccination certificate would likely be violating their travel insurance policy. I think few would see that as worth the risk.