I went back and read some old threads (from the 2006 World Cup) and Australians said that they expect Australia to be in the quarterfinals by the end of 2018. At the time it seemed realistic, with Australia just barely losing in the Round of 16, but it seems unlikely now.
Possible but unlikely. Much at the WC depends on the draw. I can see them getting out of the group stage, with a helpful group. But beyond the R16 is unlikely. The core of the team is young (average age 26 for last WC qualifier, with only 3 aged 31+) and 2018 is still 3 years away. Hopefully the players can find their way to better clubs in Europe by then and continue to improve. The will have the benefit of the Confederations Cup as well to get some good match practice and prepare for the Russian conditions.
It will be tough. Had we beaten Italy in 2006, I think we would have beaten Ukraine and made the SF. I'm really enjoying the football we are playing but it will still be difficult to make the QF's in 2018. A lot will depend on how well we can replace Cahill (a regular goalscorer).