I don't understand the application of this to filesystems. To me it sounds like it the usual way to have file icons is a simple mapping from a file type to an icon file, and in this solution that icon gets put into the metadata of the file instead of it's own file, so it's not a property of the file type anymore, but of the individual file. This couples the FS implementation to the GUI right? Isn't that horrible? If you want to change the Icon for one file type now you have to walk the whole file system and touch the metadata of every file. Also if you change the extension of the file, you have to change the icon in the metadata as well.

Edit: I would just teach the GUI to cache the icon folder in RAM.