It's never as simple as just fit GR4 with TCAS though. As GR4's fly around mostly in pairs, or more, sometimes in close formation, sometimes a couple of miles apart, the TCAS could be giving RA's so often on each other that the crews might become complacent and start to ignore them.
Is there a system whereby you could inhibit a specific response from a specific ac to prevent this? RA's from #2 could be inhibited to prevent nuisance alerts caused by formation manoeuvring.
Trouble is, that wouldn't have prevented the Moray accident, would it?
TCAS & fast-jets seem to be fairly incompatible to me, unless someone could explain how it would be used on a daily basis.