My understanding of the reasons why we are concerned as to the contents of users sandboxes and other userpages is that they are published on the Internet and available for all to see. If we created an option for editors to have a private page that only they could see then presumably we wouldn't need to police it, and that could be used by editors as a sandbox, or for any other lawful purpose. We'd presumably want to limit the space of that to avoid misuse, but I think it would be a logical extension of the userpage work.
