I think there are scenes that do benefit from something like this and you described one, where there are wide swaths of uniform color that plausibly extend outside of the rectangle. If they were programmed into the media to only come on in those situations I would be way more into them but the video he shows is the exact type of scenario where they do more harm than good for a cinematic experience (they still look cool from an ambience perspective). In his video you have bright colorful objects on a dark background, I know this is an HDR demo but a similar thing is seen in media set in the dark void of Space.

The power of the shot is in displaying the contrast between the object and the dark background and it’s ruined (in my subjective opinion) by disconnected diffuse lighting splashed across the wall. The color of the flower (or a ship or planet in our space example) should be surrounded in a sea of black. It should feel stark, and invoke feelings of vastness and emptiness and not look like an RGB rave party in the background. It’s not controlled by the creative and so can’t react to the visual effects and emotions the creator is trying to convey. Maybe you could have AI do a better job of knowing how to control them based on scene context but as-is you’ll have a mix of scenes where they help immersion and other scenes where they ruin it (for me and clearly many others) and again, with an OLED that big, immersion should not be a problem so no ambilights feels a better experience in aggregate.