This would be an awesome feature to help out with moderation and keep sensitive information private.
Thanks for your time. 🙂
You can set the reply as "unapproved" . It'll only be displayed for the post author and for moderators.
Then change the "Awaiting moderation" message to something like "This post is hidden" in wpForo > Phrase admin page. Just search for the phrase, edit and insert the new phrase: