One reason for the post edits is that it allows, for instance, someone to edit a post as they want it to be even if the time has run out and then be able to flag it for review by a mod (or maybe the review flag happen automatically) who can then decide to accept the edit or not.
I appreciate that you are making the change in order to allow long-term post editing. One of the biggest problems with the current system is when a link breaks, say, a year after the poster used the link in his post, or when the first post in a thread should be updated on the basis of later information in the thread. Of course, most forums allow unmoderated, unlimited post editing, so they've never had this problem. Personally I've only witnessed one occasion, out of all the forums I've been a part of, where an exiting forum member abused the editing feature to blank all of his posts on his way out.
Thus, as far as I'm concerned, the rule about designing the system for general use and handling the occasional exception should apply in this way: users can edit their posts whenever they want without version control making those changes accessible to their peers. If someone abuses this, a moderator can view or roll back the post to an earlier version. Simply making this one change -- restricting the viewing of a post's history to those in the moderator group -- will be an improvement. I can't see what advantage there is to allowing regular users access to it at all, no matter whether conveniently or 'with some effort'.
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I forgot to mention that I wasn thinking of adding a draft authoring option as well to allow people to author things over a period of time, saving as they go but only publishing when finished (only for topics though).
Draft authoring would be nice. I've had a number of drafts for topics that I was pecking away at, and I've had to store them in .txt files around my hard drive, or in Google Drive, which isn't much fun.