It's not re-implementing if you apply the searching, tagging, and meta-data to the file system, but rather moving those features out of several programs and into a lower-level, system global feature set. You argue against re-implementing non-hierarchical organization, but every program you mention has in fact re-implemented non-hierarchical organization as a primary feature.

If this is in the file system, then the programs that run on the system pretty much automatically inherit the organization features, and only have to concern themselves with viewing/playing/editing, rather than with all that and finding, which is ostensibly one of the primary jobs of the file system. This even has the benefit of applying the SAME search features to any application, including the file browser, so you are not constrained by your choice of organizational application. You don't have to get a script to import your old music library data (play counts, ratings, etc.) into a new player. The data is handled by the file system, so you can swap out applications or just pull up the same list of files in the file browser.