I may cop some critisism for this, but I would be very careful about any move to include GA type aircraft Cessna,Piper etc. into RA AUS. It open up a huge can of worms regarding maintenance of these aircraft, some of which are in excess of 50 years old, and have all the problems that go with this age of craft. I wouldn't mind betting that this is precicely the reason 750 kg was knocked back in the first place. I have to say I agree with MaJ Millard, keep it simple. The more complex, the heavier, faster the aircraft is, the more regulation is going to imping on our privilages. If you want to fly complex aircraft, if you want access to CTA, if you want to fly IFR or night VFR, get a PPL. If RA AUS persists with attempts to win privilages in these areas you will be all burdened with tighter regulations which most don't need or want.
Regards
Greg.