If what you want is a filesystem in a file, then it's probably best to just start with .iso files and work from there. You'd still have to standardize the direc

If what you want is a filesystem in a file, then it's probably best to just start with .iso files and work from there. You'd still have to standardize the directory structure and "internal" formats for actual data, but that would get you the filesystem-like structure you're looking for in a format that is already optimized for use as a filesystem.