'Useful life' is already less than nine years six months, as there's also the inevitable gap for most non-aviation staff between when one renews and the first trip one makes ex Oz.
Mine expired in February 2021 but unlike some I don't appear to have received a renewal notice. Perhaps a subliminal message?
The Federal (and State) Governments have huge and growing deficits but without being greedy, the Passports Office should be either extending the validity of passports (probably impossible administratively given the expiry date is stated on the photo page, and border officials overseas would only recognise that) or stating that from a date in the future, passports will be valid for say 11.5 or 12 years by Ministerial decree (assuming that doesn't require legislation, or changing of international agreements).
A third alternative would be to reduce the cost of a passport for a predetermined period by say 20 per cent, and to guarantee to only increase it by CPI each year within the next decade. But governments love cash cows.
