e.g. relate multiple recordings (different versions or remixes) to the same work (and if necessary automagically create works as in MBS-1755)
e.g. add a common performer, vocalist, ...

Supposedly, the first example is already possible for existing works using murdos' Greasmonkey script. (Doesn't work on my PC, though. )

Splitting MBS-3468 into sub-tasks as suggested by voiceinsideyou.