Better, I think, to start transitioning everything over to the new frame-complete standard now.
That makes sense if other video preservation projects join in. But that’s been asked and answered. Other video preservation projects are not joining in. So here we are, so providing compatibility releases of 4K83 seems to be a stopgap… and possibly an indefinite one.
It’s actually a lot simpler than “Each person has to make up their mind on their own.” The audio and subtitles pretty much always follow the lead of the video, in terms of timing. But the video is now leading in two different directions simultaneously, which is the root of the problem. If that were addressed, the sync issues could be resolved case-by-case pretty easily.