Such a feature would have only benefits: it wouldn't affect performance, and those concerned with storage space could easily use prunes or switch it off entirely - it wouldn't add more overhead than what "soft deleted posts" have introduced already.
Comparing revisions would be the most difficult task:
- Should it be done by showing both revisions at once and marking differences? Even for contexts only this is problematic: the "Attachments" tab is not shown by default, but if attachments are the only thing that changed then this could only be shown thru coloring the tab.
- Comparing texts and outlining only the changes is a challenge: while it's rather easy to just tell "subject and text has changed" it's not so easy to highlight the actual text portions in either of them.
The board search need to be adjusted, too:
- There needs to be an option up to with revision posts should be found.
- There needs to be an option to search within a post (and its revisions) only.