Capn Bloggs,
Stuck at 4500ft at the base of E waiting for a clearance
One of the issues for controllers in this airspace is that if the base of controlled airspace is a VFR level and there is an IFR aircraft operating within 500ft beneath it, then the controller must provide 1000ft separation with an IFR aircraft above the base.
If you are IFR and climb to 4500ft awaiting clearance then the controller must give an overflying/arriving aircraft at least 5500ft (not generally done in E because it is a VFR level and the airspace cannot be sanitised, so 6000ft would generally be the go) to prevent loss of separation (an a stand down). I believe you need to advise the controller if you are climbing to a non-IFR level, however if the restriction for a clearance in the first place is an IFR at 5000ft you can be expected to be requested to maintain an IFR level (eg 4500ft).
Also, the problem with lowering the base of this CTA is that the time you have to obtain a clearance is more susceptible to frequency congestion, and the terrain outside the 25nm MSA is above the base of CTA. On most tracks to the north of WLM, the route LSA is above 4500ft.
What would a pilot of an A320 or B737 do if, due frequency congestion or traffic, they are not visual and are approaching the edge of the MSA awaiting a clearance. Do they just climb to avoid terrain or hold inside 25nm? If not visual, the controller cannot even vector an aircraft unless it is above A066 for most of the airspace, even within 25nm. This surely impacts on the workload of the pilot, in the back of their mind knowing that they must have a contingency if clearance is not available. The controller must also be aware of pilot intentions because they still need to pass traffic OCTA to the guy climbing behind you?
The controllers will not have the ratings, tools, or airspace design to provide the flexibility and expedtion of traffic that the airspace "design" requires. This will increase workload for all involved with possible losses of SA, compounding with the numbers of aircraft involved. This will be significant at times during the RAAF Christmas stand down period and on weekends.
And I haven't even gotten on to the subject of thunderstorms close to/at the aerodrome requiring diversions/holding in Dec/Jan.