You're right the existence of shadow bans is old, but you're wrong that it's critical for a forum. Discourse doesn't use it, and Mastodon I believe is reviewable. So was Usenet. Kill files were controlled by users.
Also, Reveddit is used extensively on Reddit without subreddits falling apart. Mods of many groups will often link it to provide transparency into their work.
Also, Reveddit is used extensively on Reddit without subreddits falling apart. Mods of many groups will often link it to provide transparency into their work.