#1 - If there is some kind of controversy about the OP of a self-moderated thread, or if a self-moderated thread involves some kind of scam then this could certainly be very useful. I would say that such deleted posts should not be indexed to search engines and probably should only be available to users who are newbies and above (eg someone who is not logged in and someone who has made zero posts will not be able to view such posts). I would also say that the only way (besides typing the specific link into your browser) to access the deleted (by the OP) posts would be from a link on the self-moderated thread (eg you cannot view deleted posts from just browsing the forum).
#2 and #3 are tied together -- I am not sure how much good this would be. I think a lot of people would enter random strings of text into the explanation, especially in cases in which the OP is simply trying to keep his thread clean. Although it may be nice to get some kind of feedback regarding why a post was deleted as a poster could potentially change his posting habits in order to not have his post deleted.
I'm comfortable with having the threads of what I've envision NOT indexable by the search engines.
In re. "string of text": ONLY the worst nefarious actor would choose that ploy, for that would surely be the bane of their endeavor's existence.
To be clear, I'm not against self-moderated threads, for they serve a purpose, a course of action I've yet to utilize, of which doesn't have a thing to do with that I don't have a fuckin' clue as to how to create one.
With what I've proposed, the creator would have to give careful consideration to a post they're thinkin' 'bout deleting, for the justification on their part could easily carry more weight than just a simple deletion. Also, it could be programmed so that no two explanations can ever be the same regardless the author. And, a single word response wouldn't suffice, where, let's say, a minimum 100-character description is needed for the post to be deleted, then archived.
Here's how it would look:
Thread title: Introducing Acme's Cloud Thingie
First Post: My name is Al and I wish to introduce to you ...
Second Post: Al is a dog!
Second Post deleted now depicting the following: The author of this thread has deleted the original contents of this post of which can be viewed here: https://bitcointalk.org/index.php?board=archive
Thread title of Archived Deleted Posts: Introducing Acme's Cloud Thingie (Archived Deletions)
First Deleted Post: With apologies to the poster, I opted to delete his post for being off-topic. They're more than welcome to post in my self-moderated thread accordingly.
Original content of deleted post:
Al is a dog!
I'm almost certain theymos would have time to create such given that he had time enough to map every IP pixel on the planet.