the way i read CASA's response is that all flights are done for hire and / or reward (including cost -sharing). however because there is a specific carve out for "cost-sharing flights", one may rely on that exemption to capture it under a private operation.
sounds like the default scenario is, everything needs to be licensed/regulated unless there is a specific carve-out for private operations.
but it does sound like a PPL can't go hire a 9 seater plane and take his friends/family for a joy-ride.