I will second everything vacc1 said, everything about a future base anywhere other than Sydney is speculation and is in no way assured. Rumours are just that and until something is officially announced I would do as vacc1 says and count on being SYD based for the long term. I have also heard our cabin crew manager say that a MEL base would come before a BNE base, honestly lots of crew commute and seem to handle it just fine. If this is something you are very passionate about then do not let living out of Sydney stop you.