Wonder if the Govt realises how Wild West AliExpress is? e.g. an offer, completely unprompted, from a supplier on AliEx to invoice my item at whatever price I wanted. I wouldn't trust them to collect GST for me!
Then you lose your buyer protection. You'd need to bypass AliExpress and pay directly, as AliExpress will be doing the collection.
Keep this in mind... tax avoidance is fine, tax evasion is a crime.