Allow the Destination table in a relationship class to be a registered database view. The relationship wouldn't support any features that a view would prohibit (no composite relationships, no message passing etc.) but could be used to link database view records to a parent feature or record in apps such as Field Maps.
The main use of this feature in my organization would be to create a view of an entire archive table or branch versioned table in the EGDB, register that view, then allow users to jump to a list of archived records directly from a feature in various apps. To my knowledge there is no consistent method of relating data in ArcGIS without a relationship class in the database and this seems more pragmatic than defining a new relationship type at the Server/AGOL/Enterprise level.
