FLARM
See and be seen has been for many years the accepted AND ONLY form of collision avoidance in the majority of aviation traffic situations and the obvious risks involved has always been accepted for the lack of alternatives.
An accident such as this latest one surely tells us this is no longer acceptable. The time has come for urgent and thoughtful action.
A technological solution must be found and there are several potential routes to a solution.
European and Australian gliding use the FLARM technology (Flight alarm) which uses GPS technology to provide aircraft to aircraft proximity warning. Examples of this device cost of the order of $1000 and provide distance and azimuth information with an audio signal and a visual display.
The purpose of this is to enhance the normal see and be seen by providing a timely alert so avoidance after visual acquisition of the target can take place.
It may be that this is not regarded as suitable for the higher velocities of general aviation aircraft.
There may be other ways of achieving the same goal but why not use this one for the time being?