This seems very complex and would require significant guidance on how and when it should be done.  (Also, RelatedArtifact is really broad - it might be better to have a more tightly constrained extension that can only point to specific types of resources for specific purposes.)  We believe that such an extension should be defined in an implementation guide where appropriate guidance on its use and lots of examples can be provided.  It does not seem appropriate as a 'core' extension.