Ok, here are some broad numbers to consider:
Last year (to Sept) Australia expanded by approx 371,000 people.
https://www.abs.gov.au/Ausstats/[email protected]/7d12b0f6763c78caca257061001cc588/fa9c11f1913bdafcca25765100098359!OpenDocument

That was made up of a natural increase of some 139,000 people and net migration of 232,000.
There are about 2.6 persons per dwelling.
https://www.abs.gov.au/ausstats/[email protected]/7d12b0f6763c78caca257061001cc588/06c173caca72f27aca257e0c000e96e9!OpenDocument

Meaning that roughly there was new demand for about 53,000 dwellings with regard to the natural population increase and 89,000 dwellings from net migration.

Last year there was some 200,000 residential dwellings completed so in theory we built a little more than required.

https://www.abs.gov.au/AUSSTATS/[email protected]/DetailsPage/8752.0Dec%202019?OpenDocument

With the construction downturn, we have been expecting some 170,000 dwellings will be completed this year. This shouldn’t be hampered much by the virus as most new properties are pre-sold prior to construction and construction has been regarded as an 'essential service'.

We know that (on average) Airbnb have over 120,000 properties+ listed and that has been growing over 10% in recent years.

Since this last story was written it would be fair then to assume another 17,000+ properties have been added into the short-term accommodation pool. I'm thinking we could expect somewhere to 30K-40K attempt to return to the long term leasing market. https://www.rent.com.au/blog/airbnbs-australia

And we also know that not every property completed is available for occupation. Indeed we know that some 10% of properties around the country are unoccupied.

So, we have new demand this year of some 53,000 to 55,000 dwellings without the net migration demand.
That leaves about another 140,000 dwellings this year looking for an occupier.

The 140K is calculated as:

170K in dwelling completions
+40K in airbnb stock looking for long term tenants
- 55K in natural new demand
- about 15-17K in not available for occupation.

So, where will this surplus stock end up??

Here are some raw rental listing numbers I'll share with you...