OK, yeah, that's not quite the same as what I'm suggesting. WinFS was intended to be used at the application level. I'm talking about using SQLite (or something like that) to store filesystem metadata, more like the resource fork in the original MacOS, except that the resource fork was per-file and what I'm suggesting here would use the embedded DB to store directories (in addition to per-file metadata). The schemas would be part of the OS design. Applications would not be able to modify them or add new ones.