8 Hour would be ideal for me, 4PM to midnight. Run it on the same weekend as Clipsal 500 too, first schedule V8SC race for midday and then the second for Sunday, as per usual. Also make the Australian GT and/or Porsche Carrera AU cars eglible for GTC to boost up the grid counts.
Of course this will never ever happen but it's nice to dream a little
Let's face it, even Australian GT isn't in the best of shapes. If they cannot even attract GT3s, what change would ACO-style series/event have?