Maybe try something like Data Crow?
I was never much satisfied with the "iTunes" approach to this, wherein you get an app to "Import" some "Library" of items that you can then tag and search and comment on.
So I always ended up hacking together my own solution. Except on Haiku or OSX > 10.8, which get tagging right (in my opinion).
Poor man's solution
You can make a folder named "Tags" in your Home folder.
Then make some sub-folders within for actual tags.
And sym-link whatever you need there.
The act of sym-linking (or use TMSU) can be automated with a Contract for Files, so that "Tag this @Work" shows up in the context-menu.
That would work for a few tags, like "areas" in a GTD system, or "genres" in a music collection.
Back when I used Xfce with Thunar (the file manager), I used a Python script with a package I got out standard repos -- it displayed a simple dialog box. Let me see if I can possibly dig that up for you...
Also if the devs are reading this, Thunar had a fantastic feature -- a "Templates" folder, which populated the "New File/Folder" context-menu.