Dick - re TCAS
It is my understanding that the reason TCAS does not command a turn is because it azimuth information is too inaccurate - distance accuracy is excellent, whilst the relative altitude accuracy is dependant on the accuracy of the altitude encoders.
I have never flown an aircraft fitted with TCAS, however I have spoken with other pilots that have been in a following aircraft that the display has shown me swapping from side to side in front of them, even though I maintained the same relative position.
It is for this reason that I believe that TCAS is a 'last resort' collision avoidance device and not for providing traffic information.
Some TCAS units (Honeywell) already use a hybrid system where ADS-B ES data is used to more accurately display interrogated aircraft and to extend the range that aircraft are detected. I do not know whether it is used for RA logic yet, however I have no doubt it will be in the future.
I am guessing that Annex 6 suggests that in the future it is likely that ADS-B will be used by TCAS to allow a turn to be commanded as well. James Michael am I close?