ATC Watcher. As I understand it the sense reversal at Ueberlingen did work as intended. (TCAS can order an RA in the reverse direction to the original RA if the "master" TCAS detects failure of the other aircraft to comply iwth its RA).
But TCAS sense reversal is inhibited whenever the two aircraft are vertically separated by less than 100 ft. Removing that inhibition is one of the matters I believe is being discussed.