(if I can get GPS, video etc on my smart phone - maybe in next decade there might be an auto-TCAS cheap/small enough that could go on a R/C model?)
A few year back I had a chat with the fine chaps at CAA research who had done the work on the low power, low cost collision alerting system. The great hope for the future was in the sort of tech that leads to mobile phone location services that can tell you when a "friend" is near.