BorderForce has this power already as it pertains to dutiable items
of prescribed categories with a value over $1,000.00.
I don't have the time unfortunately to explain the entire body of legislation, but a fairly simple guide can be
found here along with the relevant legislation. I do note though that the
Schedules provide the classes of goods and the tariff rate.
At the end of the day it will be down to how many parcels they can inspect and verify given their current staff levels. Prohibited item detection is fairly simple, that's scanning and sniffing while ensuring dutiable compliance is far more labor intensive and prone to contention, review and appeal. Most likely the system will work on an origin inspect list (Ebay, big US online retailers & stores) with parcels from this origin having their invoices manually inspected for goods value and compliance and payment of the duty required by the recipient within Australia to have the goods released.
You can thank Gerry Harvey and other big retailers in Australia for their 10 year campaign lobbying the government to introduce this legislation reducing the threshold from $1,000.00.