When you edit a published document, the subject line would be [Space Name] Revised Document Type: "Title of Document Goes Here". And then the email contains a link to the post and this message: “_(insert name)______ has revised the blog post, (title of post). Click here to see the changes.”
Most documents are long enough that no one is going to read the revision in email. And even if they do, they won't be able to easily pick out what has changed. The big issue this would address is times that a document is created and has edits made in quick succession. For example, our CEO created a blog post at midnight last night. Within 2 hours, there were more documents to link it to and a few other items to further clarify or expand on. And so in the morning, when staff arrived and opened their email, they see 6 emails from the CEO. No way to tell easily at a glance what was going on. One CIO called to ask what the problem was with the Jive software that it would send so many emails from a single blog post.
This feature request would make emails more informative for users, and more obvious that it is not a "system flaw" but notification of a series of document updates.