I would like a plugin api that is called once the metadata has been finalised and written to the file.
Once the file is saved you know you have the right recording and can trust the artist, release and recording id is correct.

Example plugins that would be possible with this added:

• Manage collections and automatically add recordings to a collection of recordings that that user owns. This collection would then be available to improve listenbrainz as there is a definitive list of recordings to match listens to.
• Playlist support: I would like to write a universal playlist sharing service that you would have a list of recording id and this would find those recordings and create a playlist with those files.
• Run external tools such as submitting recordings to acousticbrainz.
• Add a plugin to follow someone on twitter as you save the recording.