And the audio and subtitle tracks have never been synced to the PAL GOUT, even for RotJ.
Not entirely true. There was a time when some dubs and subs were PAL-synced for ROTJ, but that time was short-lived and the transition was painful.
That said, for subtitles, two or three frames is irrelevant as far as sync is concerned. For audio, however, that can be a pretty nasty sync issue. I imagine 4K83 will have its own audio tracks, but for those who want to use their own audio, it will be far easier to remove frames from 4K83 than to resync a bunch of audio, some of which is available only in lossy form and would lose quality in the re-encode. I get that every frame needs preserving and think 4K83 is right to do it that way, I just see an alternate GOUT-synced 4K83 as having more practical value to the mix-and-match crowd.