It has been legal for certain preparations for some time. I bought Taki Mai Kava capsules online a couple of years ago. They are a subsidiary of this Fiji Kava company that sells on Amazon and will soon be in stores.
It's ok as long as the company imports it and ships it from their domestic warehouses, as far as I can tell. Customs doesn't even check it because it;s domestic, so there's no risk to the consumer either.
It's never been illegal to buy and sell within Australia, as far as I know. Hell, I bought a kilo of the stuff a decade ago, with no stealth packaging or anything. Couldn't have a more suspicious package of powder in a plastic brick shape. No issues. The Happy High Herbs shop have been selling a Kava extract for years (completely useless and dodgy product from a dodgy person, never buy it, it does nothing and doesn't even taste like Kava).
And actually you can buy Johnson's Kava tablets in pharmacies. Don't buy them either though.