Finally yes, lower-level Class E would require more sectors, more staff, a different rating or endorsement system for the ATCs, and probably another building. I doubt the current two centres could contain the expansion unless they move the Approach Control units (BNE, CNS, MEL, and ADL) out.
And that’s ‘game over’ for any real expansion of Australian E.
That is, of course, until the RPT collision with a ‘sport/private aircraft’ at an aerodrome in ForG, which collision will result in breathless amazement and outrage, on the part of punters, at the concept of an aerodrome without air traffic control, and a demand for action that will be difficult to ignore, politically. That’s when a version of Australian D will be introduced. Which version....
(Heard today an RPT reporting to Centre that it had to go around at YGTH, as a consequence of an aircraft on the runway either on the wrong CTAF, or not hearing or transmitting on the CTAF. The Roulette Wheel continues to be spun...)