I think we should make the data in the yellow tables on http://wiki.musicbrainz.org/-/images/5/52/ngs.png and http://wiki.musicbrainz.org/-/images/9/92/ngs-ars.png available via the webservice.

Examples:

You're using the webservice to fetch data and want to display relationships in your program. You can get the relationship itself via a query like http://musicbrainz.org/ws/2/artist/6ca1a602-c1df-408e-9f41-6ab7026a4b5f?inc=work-rels but there's nothing which tells you "lyricist"+"translated" should become "translator".

Picard, for example, might want to automatically download the country list directly from MB instead of having its own static (and separately translated) list. The same sort of thing applies to the preferred release formats - if we add a new format to the database right now, Picard has to be updated to know about it.