I think it would be very useful to be able to convert an answer into a comment (or vice versa).
Both Stack Overflow and OSQA can do this and is a very handy feature that I would certainly use a lot as a moderator
Answer into a comment - a couple of problems - what to do if the answer has fancy formatting or too long?
Should be a threshold on the length of answer that can be converted to a comment? Then, comments cannot take some types of formatting - like section headings, images and such... Strip content in those cases or just refuse to repost?
Going the opposite way (comment -> answer) is not a problem.
Seeing as how converting an answer to a comment is probably something that only a user with sufficient karma to edit posts could do, why not just give the user the ability to edit the answer (and either not allow saving a too-long comment or just truncate at the max char limit)?
It would be useful to be able to convert answers to comments, especially in the following case: user1 posts question, user2 posts answer, user1 posts other answer to thank user2, user3 would like to make the thank-you-answer into a comment to user2's answer.
Comments
@Evgeny has this feature been added to hosted sites as well? What is the process to convert an answer into a comment (and vice versa)?
@todofixthis we don't have this feature yet. I'll try to get it before the next release, this is not a very difficult one.