TL;DR:
Reviewers of a post should be able to comment on the task in a separate comment section visible to everyone but only actionable by the reviewers, 10k users and moderators.
Communication between reviewers of the same post would lead to better review choices. An experienced user might make a valid reason to close, reopen, leave closed, or leave a question open. If such reasons can be communicated to other reviewers, reviews would do their job much better.
Currently, the best option we have for this is the comments section on the post. These comments would unnecessarily flood the poster's (and any follower's) inbox. They might also be flagged by low-rep users who do not understand the concept of review, creating extra work for moderators. A non-reviewer might leave a review-like comment, potentially fooling the reviewers. Such comments might also be confusing to new users, and might even make them leave the site if a "this post is bad"-esque comment is posted. For all these reasons, "review comments" in the usual comment system might be treated as abuse.
Such comments might also be buried under several other comments or be moved to chat, making it hard for a reviewer to see them. They might also bury other comments if other reviewers agree with and upvote the review comments, going against the purpose of a comment section.
Why would a review-related comment be flagged?
In the Suggested Edit queue, comments on a review task would not be related to the post itself, but to the edit. This would be a major reason for flagging. A "This post is okay because (something)" comment would also be flagged for being outdated when the post receives many upvotes. These flags would create work for mods.
How to solve this?
I am suggesting a feature request: comments on a review task. Any reviewer of a task can comment on that task, and such comments are only accessible to future reviewers who review the task (except as an audit) and 10k users (and moderators). Such users can also post extra comments in the thread or flag or upvote comments. The same user can post multiple comments on the same task. All the comments on the review would be displayed somewhere next to the review task itself. Once a post is fully reviewed, its review comments are saved by the system, but can still be acted upon. Just like normal comments, review comments should be upvote-able and flag-able by reviewers. Review comments would be visible to 10k users and moderators in a separate "review comment archive".
But wait: what about audits?
For that, I suggest that the system stores "audit comments" which are indistinguishable from review comments on a post for each specific type of review. An audit comment can be added by any user who reviews the audit, just like with normal review comments. Audit comments from passing users are shown to the next user who is reviewing the post as an audit. Audit comments from failing users are saved, but not shown to anyone directly. Saved audit comments are visible to 10k users and moderators in the "review comment archive".
Can't meta be used for this purpose?
It can, but no reviewer would bother to check meta!
Policies regarding review comments
- Review comments should be relevant to the review task in question.
- Review comments should not be used to say "This is obviously an audit" in any form.
- Review comments should be polite and not demand anyone to do something.
- Review comments should not say anything like "please upvote this post" or "please downvote this post" or "please close-vote this question" or "please reopen-vote this question" or "please delete-vote this post" without further explanation why.
- Most of all, review comments should follow the Code of Conduct and the "Be Nice" policy.
A moderator might go through your old archives of review comments and ban you from commenting on reviews (or even ban you from reviewing), so these rules are enforceable.
Examples:
First questions: "This question isn't bad for the site because the asker has showed context."
First answers: "This answer is bad for the site because it answered a poorly-written question."
Late answers: "The only purpose of this answer was to bump an old thread. This info was clearly in the comments."
Suggested edits: "This edit adds a link which might be treated as spam."
Low quality posts: "This question is short, but it is of very good quality."
Close votes: "This question is off-topic, but has historical significance. Please flag so that it can be locked."
Reopen votes: "This question is subtly different from the duplicate that was used to close it because it deals with automorphisms of undirected graphs, whereas the duplicate deals with automorphisms of directed graphs."