A bunch of the major online sites - eBay, Amazon, Etsy, Alibaba etc. have told the Senate Economics Committee that are marketing platforms, not retailers and will not collect GST.
Since many/most merchants using the sites would turn over less than the $75,000 GST threshold very little would be collected.
Furthmore eBay has suggested that if the government tries to make them collect they will
exclude Australian customers from their sites.So implementation is likely to be delayed for a year while the government goes back to square one.
Eventually I suspect Turnbull will have it will quietly disappear like most of the Abbott/Hockey imposts.
You can read the submissions here.
Senate Standing Committee on Economics