I don't think Australia could do it on their own but bids from east Asia and that region appear to be the best alternative to Saudi. Australia with New Zealand and maybe some SE Asian countries could be a good option but the TV companies might be put of by the kick off times.
China could be an alternative but that would also make a lot of people feel morally uncomfortable.
The heat in those countries might put voters off, as assuming there is more than 1 bid, then there are 200 voting associations. And I don't see any European one voting for another winter WC in Saudi, with all that entails.
Australia could do it on their own, but probably wouldn't be allowed to, if the most recent host announcements is any guide.