Here's the Contacts editor on Haiku, BeOS' spiritual successor which is actually just a file manager window with a specific set of attributes displayed.
- filesystem could "just" store data blobs with user-defined metadata and custom (materialized) views
- querying could be done one level "higher" - no need for folders and files
folder and file UI could be just one of the views on top of that storage
- I could as easily ask for last
n images, everything linked to idea of memex etc...
- spreadsheet-like interface could be interesting as well here
- this gets even more exciting when combined with plan9 vision where everything is a file