There is absolutely no way of knowing. Will there be a fourth or fifth wave in Europe? Will Australia remain functionally closed? If not, how many seats per week? How long will the quarantine last? Will it be shorter for those who vaccinate or test out?
These are all issues which suggest that you look at this in October at the earliest. Tickets are, of course, expensive right now because there are few passengers permitted in and thus aircraft largely empty (of passengers, but not freight).
Don't forget that if you book and the flight later goes, but you do not wish to travel because the restrictions are too great, you have then made an interest-free loan to BA against some other trip which might have been better on another carrier.