@liwott
The comment is itself a creation. Just because the owner does not think it fits their conversation does not mean the author has to lose their production or the ability to show it to their own followers.
This is very debatable. Having a comment deleted doesn't mean an author loses the ability to publish to their followers. Just not with a reply on someone else's post.

Mastodon has a very opinionated approach to this by not allowing quoting posts in top-level publications, favoring direct replies, but not making the original author responsible for replies distribution either, which favors public posts.

Diaspora is the complete opposite, where direct boosts aren't allowed, other people's posts must be quoted in a new post, even if there's no additional content, and top-level authors have complete responsibility over the ensuing conversations. This favors limited-visibility publication scope and reacting to posts by quoting them in a new thread where you can have complete moderation control.

Your idea would be in-between those extremes.