Comment revision and Comment system

Every once in a while, I am faced with the lack of flexibility of the comment system of drupal. Usually it is fine enough so we forget about little features, but this one is I think worth thinking about.

User case scenario :

• Someone post a new topic in a forum.
• Someone else comments on it, as well as 10 other peoples.
• one of the 'commenter' change his comment

If no one commented on your comment, you can still edit it, but in the case of the flat list, if comments are added to the topic, some comments will always be editable, even with new comments appearing after them. So if one user drastically changes the content of his comment, the thread could be altered, and no users will be able to understand what changed.

I think this could be prevented if a message saying "edited by username on date", or in the case that someone delete his comment, we could choose to show a message like "username deleted his/her comment".

I guess that would be some work to do either with the comment module or the forum module. I would tend for the comment module as this should be possible even outside of a forum.
There should also be more flexibility with permissions for comments, like "edit own comment". Some system even have a time limit to edit messages, why not have this for comments in Drupal too ?