The best solution would some form of low power ADS-B (Mode-S + GPS vector). Three versions could be available:-
1. Low power / small and light could be fitted to gliders
2. Low/High power switchable - could be fitted to Gilders/GA etc that need to go into controlled airspace periodically (but run low power when in the open FIR to reduce power requirements).
3. Full ADS-B for GA + CAT.
This does not need to be mandated - but does need to be blessed by EASA/CAA. The key would be minimum certification for option 1 and recognition that when in that mode it is NOT suitable for operation in controlled airspace, and should not be required such high standards.
The FLARM hybrid sounds ok but is unlikely to get approval and we really need something that IFR certified aircraft can fit and use legally. Especially that could ultimately feed into the MFD.
PS. FLARM is a sort of ADS-B but uses a private radio channel.