Give RAA CTA, give them up to <5700kg, give them multi engine, instrument ratings, NVFR, aerobatic.
Now as an IQ test: spot the odd one out.
OK, let me help:
- Aerobatic: only in certified, VH-rego aircraft, so need PPL to fly
- NVFR: only in certified, VH-rego aircraft, so need PPL to fly
- instrument ratings: only in certified, VH-rego aircraft, so need PPL to fly
- multi engine: only in certified, VH-rego aircraft, so need PPL to fly
- 600 - 5699 kg: only in certified, VH-rego aircraft, so need PPL to fly
- CTA: already allowed in RA-Aus aircraft if the pilot has the right training.
Spot it yet?
So where do we draw the line? I don't know, but the list you created to indicate impending doom makes no sense.