ADS-B is a very good traffic proximity warning system, where each aircraft is transmitting its GPS-derived 3D position.
Potentially it is much cheaper, much more accurate and less power demanding than a standard Mode C/S transponder, not to mention the five-figure cost of a TCAS-type traffic warning system. It requires no ground equipment.
It sounds like Eurocontrol are doing a trial of some stuff which might one day be mandated for all VFR traffic.
I wouldn't worry about it. Nothing is likely to happen for years and years.
Does anyone know the current status of the "VFR transponder" issue? I thought everybody had to install a Mode S by 2009. I know IFR traffic needs them more or less now and I have got one (GTX330, £2500+VAT installed).