Okey doke, I don't know where they got 7,500 ICU beds as the surge capacity. The generally accepted of figure is about 7,000 (
source).
I'm struggling to see how we would overwhelm that with such a high vaccination rate, 80 percent of Australia's population vaccinated roughly equates to 100 percent of the adult population vaccinated. Even assuming that they meant 80 percent of the adult population vaccinated, that's still a high number.
If you take the recent UK experience (possibly in its early days at this point) in their 70-odd percent of the adult population fully vaccinated world, they have seen case prevalence (active cases as a proportion of population) probably peak at 1.61 percent (1.1 million active cases). If we were to see something similar here in our notional highly vaccinated world that would see us at around 417,000 active cases (presently we have less than 3,000 active cases).
The present hospitalisation burden in the UK is 6,000-odd admissions with ICU admissions running at around 850. In other words, in the UK they are currently seeing a hospitalisation rate of less than 1.5 percent, with ICU admissions running at a vanishing low 0.2 percent. Based on those rates we would have to see 3.5 million active cases to fill 7,000 ICU beds. That translates to a case prevalence of around 13.5 percent - unheard of, worse than the prevalence of malaria in India, it would be the equivalent of at least every left hander in the country being an active case and then some.
If we look at Israel, a somewhat more matured post-vaccination example, they currently have about 15,000 active cases for a case prevalence of 0.17 percent. Their current hospitalisation burden is just 280-odd admissions with about 35 of those in ICUs. That is a hospitalisation rate of nearly 2 percent (assuring not dissimilar to the UK) and an ICU admission rate of 0.23 percent (again, assuringly similar to the UK). Those Israeli numbers would yield the same sort of utterly ridiculous required case prevalence rate here to fill 7,000 ICU beds.
In fact, if you want to look at just our baseline ICU bed capacity of around 2,400 beds, based on the UK and Israeli experience, we would need to see 960,000 active cases to fill those beds. That's a case prevalence rate of 3.72 percent. On the US's very worst day with a largely unvaccinated population they only hit a prevalence rate of 2.7 percent. On the UK's very worst day, again with a largely unvaccinated population, they still didn't hit 3 percent case prevalence.
I'm pretty sure that I'd be calling bullsh^t on said expert on the radio's claim.