I've been following this extremely closely as I have a booking to Australia this year with Qatar Airways. On this page - https://www.qatarairways.com/en/trav...19-update.html - in passenger alerts, you can see how many passengers they can carry per flight. SYD is 28-40 per flight, PER is 30-35 per flight, BNE is 25 and ADL is 60. Therefore booking to Adelaide is going to have the best chance. There is no word on whether the arrivals caps, which have just been raised a little, will be raised again. It's interesting that QR say these numbers are though to 24 October. Perhaps they expect a change when the northern winter schedule comes in?

You will also have a better chance if you're a business class passenger, as the word on the street has it that people booked up front are far less likely to be bumped as the airlines are trying to maxmise revenue from the highly restricted passenger numbers. That being said, QR are offering upgrades to some Y passengers and I've seen people interpret that as "buy the upgrade or we'll leave you behind" whereas it seems like a normal enough offer that we all see in Manage My Booking from time to time.

Qatar are not selling any flights from Europe to Australia before 18 December, though they are flying all the time. After this date flights are on sale as normal. With regards to the return services, there are no restrictions, so you can come back with no problem when it comes to passenger limits.

My experience has been many changes since I booked in February. GOT-DOH-SYD-DOH-GOT became GOT-DOH-SYD-DOH-DUB (my choice!), then I switched the outbound to ARN as they pulled Gothenburg. After that I needed to change dates to take into account two weeks of quarantine and Sydney was only available via other cities, so it became ARN-DOH-AKL-SYD-DOH-DUB with Auckland to Sydney on LA. Not long after that, LATAM canned the AKL-SYD sector, so I was adrift for a few days until randomly one day ADL popped up on sale for a hot second (which I leapt on!), so now I am ARN-DOH-ADL-SYD-DOH-DUB, with the ADL-SYD on Qantas on a separate booking with Avios post quarantine. The final dates also moved twice due to flight time changes and things, so it's been some mission. Whether I make it to Australia or not, well, the jury is still out.

All I can advise you is to go ahead and make your booking and be realistic in knowing you may not actually get there. I'm fully prepared to be turned away at check-in at ARN or to be told a few days before that I've been bumped from the flight. If that happens, then so be it, I'm hardly going to throw my toys out of the pram as I know that flying to Australia is far from simple for passengers and airlines alike right now. It will just mean another rebooking and the continuation of hope.