(Following are my understanding of Australian airspace regulations at the present time & foreseeable future)
SE2 is In & Out ADSB Transponder (limited range).
SE2 can be run in parallel with a compliant ADSB Out transponder.
For maximum benefit the SE2 needs to be Bluetoothed connected to a suitable EFB display (eg iPad/OZRunways). The display will show ADSB OUT equipped aircrafts in the vicinity (10Nm +?)
For aircraft without an EFB display, there is still a benefit in that other aircraft, fitted with an ADSB IN display, will be able to see an avoid the SE2 equipped aircraft.
For entry to Controlled Airspace (CTA) the aircraft must be fitted with a compliant Transponder (Mode S, ADSB out, legacy Mode A & C). SE2 does not currently meet the standard's for entry to CTA. This does not mean that SE2 is not a valuable safety tool, especially when used in congested airspace eg Sydney.
The still legal/current, legacy Mode A & C transponders are not compatible with SE2 ie do not show up on your iPad. I presume that they are not compatible with any on board ADSB systems. In congested airspace, this makes for a real safety issue. If anything is to be made "...obsolete.." it should be the old systems ASAP!.
True our authorities sometimes impose incredible stupid/impractical/ineffective regulations on us, however I cant see the aviation authorities making "...Sky Echo units .... obsolete..." any time soon, as this would be a significant backward step, in their current drive towards the (subsidised) fitting of ADSB systems in small aircraft.
I doubt that SE2 will be made obsolete, :
As it does not conflict with ADSB Out
If the sole transponder on board, as long as the aircraft/pilot does not wish to enter CTA π