The specification is here:
http://specifications.freedesktop.org/mpris-spec/latest/Track_List_Interface.html

GetTracksMetadata and GoTo methods are fully supported. AddTrack and RemoveTrack are not supported since we use Tracker and can't add and remove tracks. CanEditTracks is always 'False' because of the same reason.

TrackAdded and TrackRemoved are not used because the data needed in TrackRemoved is unavailable immediately after the row in the GtkTreeModel is deleted (iter is not available in “row-deleted” signal). Instead, each add and remove emits TrackListReplaced. This is acceptable behavior according to TrackListReplaced's documentation: "It is left up to the implementation to decide when a change to the track list is invasive enough that this signal should be emitted instead of a series of TrackAdded and TrackRemoved signals."

TrackMetadataChanged is not used since the views reload when metadata changes and we can't easily track them. Music doesn't have a tags editor anyway.

Note that I have tested this manually because the GNOME Shell extension that I use for MPRIS doesn't support MPRIS TrackList. I've checked the behavior of Rhythmbox and VLC Media Player for comparison.