We are in danger of loosing the plot here, TCAS is far too expensive & heavy for fitment to small GA types so is a non starter, it should also be rmebered that Two TCAS equipped airlines collided over Switzerland a few years back.
ADS-B probably is the best answer, the UK CAA has been moving in that direction ( albeit hindered by EASA ) and awairness equipment like FLARM is avalable and widely used by gliders and the more forward thinking in powered Aircraft.
Even if the take up of such equipment was 100% there would still be a risk. The last thing we have to deal with is the civil liberties types who object to broadcast their position on privacy grounds............ I wonder what the civil liberties issues of being six foot under the ground are ?