To add to Narada's excellent list of links, there's a big EuroControl project on ADS-B with lots of supporting documentation:
http://www.eurocontrol.be/projects/e...ds/default.htm
Part of the problem of TCAS for GA is the directional antenna requirement. The BF Goodrich Skywatch system is a TCAS that's aimed at the bottom end --
AFAIK it doesn't meet the relevant standards for air carrier use. And even that is probably too big to put on a sophisticated single, let alone a microlight or glider.
I'm convinced the answer lies in ADS-B and similar.