I think it would be great if an administrator can run a NXQL query with the rights of an other user.
Joe ask to the Nuxeo administrator why he doesn't see the "confidential" workspace
The administrator check the rights of this workspace, and can see that Joe is allowed to read and write
Then, from the advanced search panel, the administrator can run a NXQL query like :
AS Joe SELECT * FROM Workspaces WHERE dc:title ILIKE 'confidential'