The subject of downlinking RAs is highly debated in some circles.
IFATCA is against it on time the info will take to be displayed , the info might no be correct any longer , and on legal issues. ( as a controller is not supposed to do anything anymore once he knows an RA is in progress ).
IFALPA is for ( they even presented a paper to the last ICAO ANC on it ) arguing that it is complementatry to R/T.
The Japanese intiative is purely a domestic Public relations issue.
Their near mid air near Tokyo in 2001 was due , in great part , to one of the pilots electing not to follow the RA, so dowlinking the RA to the controller would have confused the issue even more.
The Ueberlingen collision last year , the clearance was issued BEFORE the RA , and no more instructions were given after the RAs started. so downlinking would not have changed anything procedurally. And by the way, downlinking an RA to ATC will mean an RA has been triggered by a TCAS not that the pilot actually is following the RA ( in Europe, 40% of pilots still do not follow RAs according a 2000 -2001 Eurocontrol Bretigny survey ) so little use for controllers.
The only solution for me to the TCAS / ATC interface is a procedural one. ICAO will issue later this month clear guidelines for pilots that should go a long way in clarifying the situation.
Downlinking RAs will not resolve the problem.( especially since the Japanese "trial" will apparently not downlink the sense of the RA, just than an RA is triggerred )