'TCAS would take over only once ATC had failed the mission'
Oh really,I think you'll find it covers a lot more than that UNCTUOUS.
It's probably me,but the article talks about sharing/accessing TCAS info,you seem to have assumed that the ATCO will have the ability to override TCAS,not sure that is the reason at all,FINDO's points,show some of the current shortfalls that might be helped by such air/ground sharing of info.