From: Northwestern Georgia, USA
With an all out commitment by Japan, I believe Oz can be taken. In fact, as an Allied player, Oz worries me considerably more than India (and India would worry me alot under the right circumstances).
NE (Townsville) and NW (Darwin) Oz are easy pickings for Japan. Even the Perth quadrant should be easy. The tough nut, of course, is the southeast quarter. If Japan can land in strength at, say, Geelong (or Portland) and Newcastle (or Maryborough) and move expeditiously to invest Melbourne and Sydney...well, the Allied player is going to sweat.
You know this, but you'll need to move fast, before your opponent can move in reinforcements from the USA. And you'll need the KB to impose a blockade.
And is there any reason not to bomb Aussie industry, especially aircraft factories?
Yes, Oz would worry me if I was an Allied player facing an aggressive and experienced opponent....