Whew. That could be interesting. Maybe a little too interesting if people can get into arguments and then go back and revise their posts to support their arguments and claim, "I didn't say that". My suggestion would be to handle edits the way revised threads are handled, with a link to the original "as is" post.
Nice work on the forum. Tip of the hat to you. Even somebody like me who is old and confused and set in his ways can use the forum just fine.
it will likely be timed. After 5 min, it will then be disabled or something like that.