I think a more clear name for this would be "filesystem data structures" since the key idea is editing structured data through the filesystem. I can imagine a FUSE driver that can map many types of data to this structure.
Yes... "metadata" is becoming an overused term. Not all data is metadata.
My first thought when I read the title was about those .nfo files used by Kodi/Jellyfin and other media centers to keep information relative to the media files.