Currently, the submit button only submits AcoustID fingerprints to the AcoustID service (afaik).

This means that users are unable to submit to any similar service, and that developers of these services can't obtain data from Picard users. It also means that AcoustID is the only service that Picard can use to scan tracks with no metadata (again, afaik).

The submit button should be extended to allow submissions to multiple music identification services at once. This could be done by allowing service developers to create submission scripts, which are automatically called when the submit button is pressed. This system could work in a similar way to the existing plugins system (or even be an extension of the plugins system).

A core set of submission scripts should come with Picard (AcoustID included), so that no existing core functionality is lost.

Picard should also be able to perform lookups on several services - the user should be allowed to specify a default service - Picard would then attempt to lookup using this service, then fall back to others is no match is found.