Yeah, that's what I thought.
That email exchange was not about whether a SkyEcho2 was a substitute for a TSO'd transponder, per se. Clearly not the case.
It was about trying to get clarity on the meaning of the following limited exception:
AC 91-23 v1.0 "Apart from an integrated TABS device able to substitute for a transponder in Class E & G airspace
Thus the issue came down to the definition of "integrated TABS devices" and it turns out that I had misread part of the CASA docs in that regard.
That is what Matt from RAAus corrected me on. But even in that exchange we did canvass the related issue of whether IFR cockpits had to have ADSB-IN CDTI (cockpit display of traffic information) which, I believe, they (still) don't and whether ATC filters out EC devices, which, I gather, they don't anymore, necessarily. Those are what seemed to be the sticking points for ECs in E, rather than any perceived inadequacy of the SE2 to do its job as advertised.
However, I thought maybe things had moved on when you were suggesting that a SE2 might be okay as a 'tail-light' in Class E.
(I think I might have missed your drift ;- )
Anyway, seems we all agree that the great unwashed need to stay well clear of the upper E classes unless carrying a transponder that will definitely trigger TCAS and definitely be seen by ATC. At least until ADSB-IN CDTI is mandated for all IFR flights (as is already the case for ADSB-OUT).