I certainly can't argue that one would never have a valid reason to
reference content in another diagram or outside of the topic. However, what
I can argue is that the DITA Specification from 1.0 up to the latest draft
says that the target of these references should be in the same diagram, and
that as such it's not really something worthy of a last-minute change in
the 1.2 specification. I don't think that the missing keyref was an
oversight, and thus wasn't a bug - it went along with the previous
description and understanding of the elements. It's always worth discussing
when something in the spec seems too limiting, but that doesn't mean that
the existing markup or description is broken.
For this specific request - to add keyref to
