Logic for finding all references to an Identity (e.g., 'Where Used" or "Item is referenced")?

When a user (alias identity) is no longer active we need to determine where the identity has been referenced in both standard ways like group memberships, activity assignments, etc. - as well as custom usages specific to our applications.  

Existing mechanisms include 'Where Used' which is TMI; and attempts to delete generates the system error 'referenced by another item'.  

One approach would be to refine the results of the "Where Used" query logic to specific areas where admins can gracefully retire usage of the departing Identity.  

John Sperling mentioned a configurable Where Used and Structure Browser at ACE 2024.  I haven't heard of this being completed, but getting information on the generic query to find all references would help tremendously.

thanks in advance