The fundamental issue, though, is not how aesthetically pleasing Person X finds it, it's the fact that by doing it the project would cease to be a preservation effort and become a complete fan edit.

He would not be restoring or recreating the original grain structure, he would be introducing an artificial effect purely on an aesthetic whim. The issue with wiping grain from film is not only the fact that you remove the visible grain structure (which when present contributes to the film-like projection appearance during playback) but also because you remove fine detail by wiping grain - there's no way around it. The detail that's absent due to DNR is gone forever. By introducing artificial grain he's exacerbating a pre-existing issue... he'll be further obscuring what fine detail remains by adding an additional layer of artificial noise. Not only that, it won't be a representation of the original grain structure, it'll be an arbitrary artificial after-effect.

It's best to work with what original grain structure still exists. Adding artificial grain wouldn't make the presentation more faithful (it would neither be the original grain structure nor would it restore the fine detail caused by scrubbing out some of the original grain,) it would make it worse overall. DNR is an issue with the BD release, but it's not as if the original grain structure has been entirely eliminated (like in the new Predator release for example.)