Slight problem though: the ATO doesn't care what you or I think bitcoin (and the other cryptocoins) are or are not. If they audit you then only their interpretation matters.
Agreed. Although it is a self-assessed tax, so people will need to form their own view (or go for a ruling) before an audit occurs.
I expect the ATO won't have a problem with people paying GST when they spend or trade Bitcoins!
If the ATO does take the view that GST applies, then a legislative change would be required to change that. The change would involve the Government, on advice from Treasury (not the ATO).