This jsfiddle, reproduces the issue I'm seeing in my website that uses the relational data layer of EnyoJS 2.5:
I have two collections (in the example "books" and "authors") that have a relation ("books.author" -> "authors"). I then attach an on-any-event-handler on the books collection: this.$.books.on("*", ...)
While this handler triggers on normal attribute's changes (e.g. the "title"), it does not trigger on a change of the relation's key (the "author").