Australia doesn’t use IBAN as far as I know, so all transfers will need to go through SWIFT.
When @anon33247966 said you will have IBANs just like all existing users, it means you’ll be able to get a euro IBAN (GB*) (+ probably also a local UK account)
It’d be great if they could provide local USA transfers using ACH and the same for other countries like Australia, but I doubt it’s even in their plans … Foreign transfers are often a real pain and the SWIFT network is far from the best.
I guess the best way to avoid fees for the people from Oz will be to simply top-up using debit card (0% fee) and pay directly with a Revolut card.
Edit: you might want to try using TransferWise’s borderless account in the meantime, I just checked and it’s possible to get a local Australian account (BSB+account number), which means you could load through them for free and then send that money anywhere in the world 
