So far my idea is that this would be exposed in the album view in the library - you could show line segments connecting songs which have been "grouped". This would make the state obvious and also provide a convenient way to multiselect and toggle grouping. Also when a song comes up solo (perhaps because the user chose to do so) since there is no where to draw a line segment to it would simply have a dot in a predictable location to indicate that it is missing its sister track.
Yeah I like the idea of representing the linkage as chain links.
Then you could show a broken chain link if a linked track is shown in a view by itself sans sibling(s).
That type of UI would be simple enough when you want to link tracks that appear in sequence on an album. Are there any use cases for the ability to link unrelated tracks X Y Z together? Probably not. Playlisting pretty much covers all that functionality.
