So, the bottom line...
Is there a system superior to the FLARM-type system, which A) does not require a power source other than battery, B) costs as little as the FLARM and C) is always effective in alerting to nearby traffic?
If there is, then tell us about it. However, I havn't seen one - transponders and their receiving equipment are costly (particularly the active receiving boxes - 10,000-pounds) and consume a lot of power. ADS-B and ADS-B receivers will probably be similarly expensive and power-hungry. Neither, as far as I can see, could form a system capable of being fitted in all light aircraft at a low enough cost.
There will always be some new 'wonder unit' just around the corner. But some time, we need to take the plunge and settle on one type of unit. I understand that there are a number of companies producing FLARM-compatible equipment, so there is no monopoly problem. Maybe making them mandatory is a bit radical, but strongly encouraging their use by various means, perhaps followed by making them mandatory, would seem to be a good idea. They seem to be proven in the gliding community.
Any thoughts?