ATC Watcher,
I should have written : " Determining the position of other aircraft based on R/Tto obain situation awareness is not required in IFR .. "
Sorry, I can't buy that.
I've averted 2 serious loss of seperations (1. a/c cleared to same level, 2. a/c cleared through my level) by having SA regarding their location relative to me, and talking to ATC pdq! If they had been talking in french I wouldn't have caught either event, resulting in an airprox at best.
Every part of the system has the ability to add safety.
CPB