I was a TV critic for the London Evening News in the 80s and so I saw Threads a few days before broadcast. It was projected in the small movie theatre used at that time (at the British Film Institute? Not sure.)
I saw it right through and have never forgotten it. Nor have I forgotten what happened at the end: an audience full of hard-bitten hacks sat in absolute silence for about a minute. Nobody talked as we walked out.
I remember the Radio Times cover for that week as well, branded on my memory: a traffic warden, in uniform, bandaged, carrying a gun in a wasteland. Brilliant piece of imagery.
I heard later that Threads was shown in Russia - although the makers refused to allow any cuts. I honestly believe that Threads helped Glasnost.
Yes, Threads should have another global release.