There really should be a way for users with the (changetags) permission to be able to remove tags from deleted revisions. This would be especially useful for sites where pages in certain namespaces can't be undeleted once deleted.

There are some sites out there that have restricted the ability to undelete pages in certain namespaces, but haven't restricted the ability to delete pages in those namespaces.

Not being able to remove tags from deleted revisions is a real problem for me. As one of the wikis I administrate have 9,648 deleted revisions to remove a specific tag from before the software will allow me to remove the tag from the remaining 5,000 revisions.