Gentle Flyer....
when you say “For what ASA had proposed 5000ft is not good enough” are you saying the proposal is flawed based on the ADSB coverage at 5000 ft published by AsA OR is it the definition of the published maps inadequate and the fact we do not have coverage diagrams below 5000?
To clarify, I believe the ASA proposal has been undertaken in haste, hence the many holes in it and the huge industry response. For the proposal to work they must have adequate either Radar/SSR or ADSB coverage at those locations that have significant IFR traffic. Industry has not been given that information and in fact for some locations, I would be surprised if ASA knew what it was.
We do not know what the ADSB coverage is at 3000ft because ASA have not provided that info. We do not even have a list of locations where there is an ADSB facility to help work it out ourselves. For Class E to work at low levels and to avoid procedural separation with associated delays, I suggest that the existing Class G procedures work ok and there is no real need to drop E to 1200 agl unless there is appropriate surveillance at the lower levels. If that can't be done, and the risk justifies it, then the answer is a class D tower at those locations that have traffic to justify it. Maybe there is only one such location in the whole J curve?