From reading the PFA and BGA responses to the Mode S proposal it appears that the French and the Germans are NOT proposing to make transponders compulsory in open airspace, but only in CONTROLLED airspace (which makes sense because all concerned will be in touch with ATC anyway)
The CAA seem to be alone in the folly of wanting everything that flies to have transponders in uncontrolled airspace.
I wonder what would happen if every light a/c, glider, microlight, VLA etc had a transponder and then asked for RIS in open airspace. How long before the system collapsed? 5 minutes??