As for the public forums, nope. not going to happen... Only the author and forum moderators will be able to edit topics. This is mainly because vBulletin, and other forum software, weren't built for this kind of access. I'm sure you could get around it with a hack, but i'm not too fond of most vBulletin hacks, as most of them directly change the db.
Besides my technical objection, I really think it wouldn't be a smart idea to let multiple people edit posts, I would only make it harder for staff to track who edited what exactly.