The report on the mid-air between G-JAMM and G-WACG makes tragic reading. The chance of the two aircraft being on such similar and converging tracks where neither had a chance of seeing each other is, I guess, very small. That said, in a world where autonomous cars can now routinely detect and avoid multiple hazards in highly complex environments, it can't be that challenging to develop and mandate an affordable, universally compatible solution for two aircraft to detect each other in otherwise empty airspace.
The report concludes: "work is ongoing, led by the CAA, to promote the development and use of compatible Electronic Conspicuity (EC)aids to help mitigate the well-known limitations of ‘see and avoid." It's no help at all to this tragedy, but I can't help thinking that if Elon Musk (for example) had happened to turn his mind to light aircraft conspicuity, such a solution would have been designed, developed, promoted and installed in all GA aircraft some years ago.