I don't know anything about SMF, so I don't know if there are any mods available to do something like this, but I had an awesome idea to deal with the minor problem of edits.
For the most part, edits aren't a problem at all, but I know complaints arise periodically when someone decides to change or delete a post. There have been suggestions and changes made in the past, like implementing a time limit, after which no edits can be made, etc. But is it possible to have an edit history (kind of like what Google Docs does to allow multiple people to collaborate on the same document simultaneously)? It would be really cool if you could click the "Last Edit" tag and be taken to a version history that would show each version of the post. If the user clicked the modify button five times, all five versions would be there, time/date stamped. It would be especially cool if all of the text that varied between two versions would be displayed in red, or something, so that you could tell at a glance what the edit was for.
This way a person could edit his post as many times as he wanted, but he can't actually delete or change something for the purpose of keeping others from seeing it later on. I edit my posts a lot, sometimes long after I posted them, but only for spelling/grammar/clarity. I'd love it if any time someone suspected that I was playing fast and loose with the facts they could just click a link and see what I had changed.