As already proposed on the mailing list ( http://lists.musicbrainz.org/pipermail/musicbrainz-devel/2015-May/006108.html ) I would like to propose to create a new Scrobbling feature for Musicbrainz which would enable registered users to store their music playback in the database.

For the new table we would probably need the following entities:

userid
datetime
recording

Updates for a given user would be performed by various hard- and software music players using the given Musicbrainz account. Of course it would be nice to add further user services in the future (like automatic publishing of played titles to various social media, etc.)

Further I propose to add a privacy setting for each user (probably user table) which could have 3 types:
1) It is ok to have anybody access to my scrobbling and rating information (with a link to my user account)
2) It is ok to have anybody access to my scrobbling and rating information but only in an anonymized form
3) Nobody should see what I scrobble/rate without knowing my user name and password

The appropriate raw scrobbling and rating information should then also be exported in database dumps, with scrobbling and rating information left out for users with type 3. Users with type 2 will have their userid removed in the dump of the user table - if possible - thus rendering the assignment of a scrobbling/rating invalid (the user ids in the scrobbling and rating tables need to be unchanged, because even if the recordings can't be assigned to a specific user, it is necessary to assign them to a single individual user though). If this is not possible the user table should get another id, which contains an anonymized userid which will be used instead (or the userid is set to an unused value)

As default (also for existing users) I propose to use type 2.