I somehow don’t seem to get the problem here 😉
I do have a SMB (CIFS) share on my NAS (using standard Samba), so I can use any ID3-Tagger (or Vorbis-Tagger or whatever) to change every file I like. Granted, I have to tell Firefly to rescan, or wait until it does this automatically, but with so many tagger applications out there, and every NAS having a way of accessing the files through the filesystem, isn’t some interface for “remote tagging” directly through Firefly a bit of overkill? Samba is a specialist in file networking, and there are a multitude of specialists in tagging, so why re-invent all that (unless iTunes would directly support remote tagging, which it doesn’t)?
Speed may be the only reason – rewriting a file over a network connection may be slow through a NAS. But if you use an intelligent tagger that creates tags with a bit of padding, it’s much faster.
I have just re-tagged my whole collection (nearly 20.000 songs) through a Samba share and ID3-TagIT and TagsRevisited, adding album art, artist URLs and fixing Genres, without any problems arising. Can’t put this into one of your scenarios though – who can edit and who not is not just “one” or “all”, but exactly those I give write access to the Samba share, making it possible for one person to add songs and update tags, and for others only to listen, just as I want.