FLARM does not appear to have a future in mainstream European GA because it has no ICAO and thus national CAA backing.
ADS-B is "coming" but it will be implemented using the Mode S data channel, known as 1090MHz Extended Squitter.
So if you have say a GTX330 Mode S transponder, and connect it to a GPS, it will radiate your lat/long. This already happens on airliners' Mode S installations but the resulting system is classified as Enhanced Mode S which is a certification issue for GA which currently uses Elementary Mode S (which AIUI is not permitted to radiate any parameter at all).
Then you need an ADS-B receiver and I don't know how that will be done. Maybe a GTX330 can do that bit too?
ADS-B would work well because it uses the GPS position which is ultra precise, and won't need the complicated direction-sensing multiple-antenna and very expensive installations which present-day TCAS systems need. In principle, a cheap PDA fed from a 1090ES receiver could act as your "TCAS".
But it is all many years away, in Europe, and as always there will be exemptions for VFR which will make it to a large degree worthless.