After writing Identifying Subjects with Facets, I started thinking about the merge of the subjects matching a set of facets. So the user could observe all the associations where the members of that subject participated.
If merger is a matter of presentation to the user, then the user should be able to remove one of the members that makes up a subject from the merge. Which results in the removal of associations where that member of the subject participated.
No more or less difficult than the inclusion/exclusion based on the facets, except this time it involves removal on the basis of roles in associations. That is the playing of a role, being a role, etc. are treated as facets of a subject.
Well, except that an individual member of a collective subject is being manipulated.
This capability would enable a user to manipulate what members of a subject are represented in a merge. Not to mention being able to unravel a merge one member of a subject at a time.
An effective visual representation of such a capability could be quite stunning.