Update for Northern Ireland 1939:
I'm just off the phone from someone at PRONI who called me for more info regarding my request for an address in Belfast, which is apparently the first they have received, though they have confirmed that they have received several more since - so many that I was told "we are going to have to do something about this".
They have found the info for the address I am interested in. There are 794 registers, two to a box, all completely unindexed and stored in an out storage facility. By a sheer fluke, my address was in the first box they looked at. The person I spoke to was very friendly, but did not know too much about what has happened in mainland Britain regarding the equivalent registers here, so I've e-mailed a summary of all the developments that have happened so far, starting with Guy's FOI act, the Scottish release, then the new NHSIC system etc.
Because the GRONI has to be consulted regarding permission to release the material it was suggested that if I could send information on proof of death, it would help with their discussions. I have therfore scanned a death cert for my grandfather and e-mailed it over, along with copies of English and Scottish 1939 releases I have already obtained, and I have explained how both the systems work over here.
In summary - I think this is a big deal for PRONI, but I also think they are extremely sincere about dealing with it. I've been asked to leave it with them for a short while, as various negotiations apparently now have to take place. But it is looking promising.
Chris