Following a forum discussion(1), I suggest to have a screen to manage attachment history like we can manage page history. This screen should:
- list all available revisions for an attachment (like today)
- allow to download / view a particular revision of the attachment (like today)
- allow to delete an attachment revision (new feature).
Option: when deleting an attachment revision, XWiki could inform the user which page(s) revision are "using" the revision of the attachment.
(1) see forum thread: https://forum.xwiki.org/t/delete-old-attachments/5049