Good Question.
Whatever the answer is, in my view the solution is not to import a cobbled together system that has developed over many years with operational and political imperatives, to replace our own cobbled together system that has developed over many years with operational and political imperatives, purely because a couple of people say it's better but can't prove it with any real data or objectivity.
A good start would be taking the politics out of it - as much as possible.
Capacity restraints in Australia, where they exist, are to do with terrestrial infrastructure, brought about by privatisation of airports more than anything - the Airspace itself is not constrained, and nowhere near becoming so.
Personally, I have seen no convincing impartial evidence that airspace 'reform' as decreed by the Smith/Higgins POV is going to 'revitalise' GA / Aviation in Australia - whatever that means.
But hey - WTF would I know? I ride a Malvern Star.