Mea culpa: allowing users to systematically admit mistakes. A great idea! I'm surprised by the depth of thought that went into this idea ("But what if ... ?"). Many of my own mental objections were answered in the article. That in itself is an inspiring template for tech feature proposals!
One thing I'm wondering: if replies are disabled, are the original replies also hidden? If the original poster doesn't want to "follow up", then future readers can construe the reason for the mistake by reading the original replies.