Mstn 17 has introduced Auto-update Parametric Cells. It would be good to extend this to any 'hidden' models in the dgn file. Shared and Parametric Cells are stored in a hidden model in the dgn.
User selects elements to be published. Ctrl-Alt-G saves a copy of the elements to a hidden model, uses the Dependency API to associate a callback to the copied elements in the hidden model. When the original elements are modified, the call back updates the hidden model. Tentative, active ACS allows the user to define a new coordinate system for the published elements.
User is in another dgn or model and Ref attaches the dgn with the published elements (in the hidden model). The Ref attach dialog lists the hidden models under 'published'. User gets to Ref attach the published elements or alternatively place as Cell using the Place Cell dialog.
The regular Ref attach, Auto-update functions work as normal to support cross-file updates.
See MCAD apps like Siemens NX etc for how extracted, associative copies of geometry etc are regularly used.