Sorry but this argument makes no sense. First. DPI is a print construct, and has nothing to do with film. If you’re talking about pixels, then it shouldn’t be conflated with DPI, which is strictly about translating pixels into printed dots on paper (or similar materia)l.
That being said, the FADGI standards for motion picture scanning haven’t been updated in 9 years, and were originally written when it wasn’t even possible to do high res scans on small gauge film.
The notion that “there’s only x resolution on the film so there’s no point in scanning it at a higher resolution” is an old and tired argument that needs to die. It is a valid argument when you’re talking about low res scans. Standard Def doesn’t do small gauge film justice at all because it’s not able to resolve the image that’s on the film. But other factors than the film itself come into play that that argument doesn’t consider.
I agree with you that there’s a point where it probably makes no sense, but we won’t reach that point until we’ve gone well beyond the capability of modern display systems. Right now televisions are 4k-ish so a 4k scan makes sense, to avoid scaling up from a lower res). If televisions make the mainstream jump to 8k (I don’t think they will because it’s really unnecessary in most situations), then an argument can be made for higher resolution scans to match, otherwise your 4k scans will look soft due to the upscaling.
Additionally, oversampling and scaling down has multiple positives that come with it - one is sharpness, but a bigger one is that you can oversample an image made with a bayer sensor camera, and downsample it so that you have effectively the same thing as a scan done on a true RGB sensor. That makes an argument for 8k and higher scans viable now.
I mean, even in the very early 2000s, the Northlight scanner had a 6k sensor, for outputting a 4k image. While you could scan to a 6k file back then, it was never meant to - it was designed to take advantage of oversampling. And that wasn’t a bayer senor, it was a very good RGB trilinear line array