The load out of Australia is woeful because of the restrictions on leaving the country, and load into Australia is woeful because of the strict cap. I really feel sorry for airlines and I do not blame them for prioritising higher revenue passengers. So, if you want certainly, book the most expensive fare you can possibly book. (Saying that, unless the trip is really essential, I'd feel bad about taking a seat off the people who have been waiting for a very long time to get back or those who are desperate to go there for compassionate reasons.)

As for BA, unless they get a cargo contract into Australia that is sufficient to operate the flight with almost no passenger, I am guessing it would be very unlikely for them to be operating to SYD any time before the cap on arrivals into Australia is raised substantially (I'm talking being raised at least 5-fold) so that they can operate viably.