This isn't actually a bad idea. Although I think Theymos was more in support of retaliatory feedbacks as a form of replying rather than being able to actually reply directly... And as the others have said, it would make the page look a bit messy.
Maybe a small link with the response, similar to how reference is currently used? I think grouping feedbacks left by a user and having an expand link to limit the number of lines viewable by default in the comments would also clean up the look a bit.