This quote from Harris suggests it’s the latter:
There seems to be a misunderstanding, at least in online discussions, as to what HDR (High Dynamic Range) actually is… and might not be.
It is NOT an inherent part of the 4K UHD package.
It is in no way necessary toward the enjoyment of 4K, either in the home, or elsewhere.
HDR is an option, much like ordering a different kind of leather of fabric for your new car’s interior.
It’s nothing new – been around for years.
If generally NOT a part of the design of a film, with most HDR entering the picture, no pun intended, during post., e.g. “Wouldn’t it look neat if those flames were really bright orange…”
It’s added the same way that 3D is added in post, to the majority of 3D productions.
It has no relevance to production photography.
It should not be included as a function for classic films, unless the filmmakers have a desire to re-visit, and create a new version, a re-imagining.
It will not work well with most classic films, and can be problematic to those that have needed restoration based upon fade.
Want to see 2001, or Lawrence, Ben-Hur, The Godfather, The Magnificent Seven, or Elvira Madigan in 4K?
No problem.
We’re ready for it, and there’s no reason why those films can’t be released, except those which don’t fit on the current sized discs.
And NONE of them should be released with HDR.
Every UHD release does NOT need HDR, nor should they have it.
If we can clear the airwaves of mis and dis-information regarding HDR, things would be easier.
From https://www.avforums.com/article/forum-topic-should-old-movies-get-hdr-releases.13707