In adding my comments to this thread, I am actually surprised at the number of people agreeing with each other...and me with them.
Tobzalp, I think I actually agree with most of all. If it flies, it should have a transponder squawking a discreet code and a TCAD or TCAS capable of responding to a resolution advisory.
Why?
Because Australia doesn't have enough radar coverage and too many people these days have their heads down at g-whizz shiite in the cockpit.
Dick Smith Actually has a point about technology. We might benefit from ADSB on a broad scale in the future, but TCAS and transponders are both here and now.
I say mandate TCAS for all turbine operations due to high rates of closure and be done with it and TCAD for all piston.