A discussion with someone from AsA revealed the other considerations.
Basically the change means the controller can only handle six (possibly seven) on their frequency. Who knows what will happen, but that is their current interpretation. If six are 'in the circuit', which can include some inbound and outbound, and then someone extra calls inbound, they will be required to hold at the inbound reporting point - they cannot enter the control zone. This is a crazy situation making the whole situation far more dangerous.
It is not uncommon for two even three aircraft to arrive within 2 mins of each other at an inbound reporting point. Now will they be required to orbit OCTA awaiting a clearance? Very very poor situation increasing the risk of a collision. CASA, you will have blood on your hands.
Furthermore, consider the VMC criteria required when GAAPs become Class D aerodromes. Being clear of cloud will not be enough, you will now require 1000ft vertical sep from cloud. On days when a 1500ft cloud base would have easily allowed flying (maybe restricted VFR) we will all be kept on the ground.
Yes, CASA went to the industry to find the problems. But did they talk to the stakeholders about these changes - pilots, flying schools and AsA?
It may please the smaller operators, but don't be surprised if a number of medium to larger schools walk away from the GAAPs.