Caucatc: You may also wish to consider that there are many pilots who will ignore ATC during a TCAS RA. After all, it was probably an oversight/foul-up in that ATC system the caused the RA in the first place. It is also my understanding that once I'm instructed to perform a TCAS manoeuvre, the system expects that I'll maintain my existing heading. I'll also wager that it would be a bugger for ATC to give any sensible headings to traffic involved in TCAS RA's.
PM