Currently we only have an order of precedence for catalogs as they apply to dspMonitor but this doesn't work well for the reports in a repository as each repository may be for a different system type. Out of the box we deliver some SAP reports so the SAP catalog is in play even if we don't actually have SAP in an active repository. Assigning a catalog at the repository level seems like a best practice to me.
This is a great suggestion. Further investigation will be done to determine whether this is feasible within the framework without impacting other applications.