There's also the fact that it might be best of Rockbox didn't modify your audio files in any way, as that greatly decreases the possibility a bug could ever damage your music collection.
A solution that may be better would be to request the developers of the media management program of your choice include support for both generating and reading the Rockbox database. Then they could import and export ratings from Rockbox as they pleased, as well as provide better syncing options to Rockbox by allowing their software to generate the database quickly at time of sync.
Another great idea.
It would be good if it was possible to manage a Rockbox'ed DAP through some well-known open source music player that has a library (e.g. Rythmbox, which comes by default on Ubuntu).
The result could be something like Rockbox utility (which installs and updates Rockbox and its extras), but also synced music, everything from inside the (software) player. Rythmbox supports syncing and initializing standard iPods which are closed platforms, so I don't see any problem in supporting RB installation/update as well as DB sync and AlbumArt extraction (from the files that contain it, or even downloading from the internet) on the RB-capable players that support USB. Perhaps something that could be done in a Google SoC?...
The biggest problem of coding these fancy features, is the usual: until there is somebody interested on doing it, both from the players' devs and RB devs, it won't be done. I talk for myself, I don't need music sync in any way and I think most of the Rockbox devs don't need either (I usually only copy/delete the files by hand). But, the users used to programs like iTunes, or users that have a large collection of music which changes frequently, would enjoy a syncing app for sure.