Interesting thread!
A suggestion would be to publish a coverage chart based on FBW's knowledge so that plots could, if they wished, plan their flights to remain in areas, or at altitudes, of known coverage. Of course some jobsworth would moan and claim they could not contact Scottish at 2501 ft in an area promolgated as good above 2500.
Some pilots won' t use radios, at present that is their choice, but even if coverage is poor in an emergency, 'someone' on the frequency might hear enough to get the SAR ball rolling.
Keep up the good work FBW