Ok.
The following idea is beyond my current knowledge of phpBB3, so it might not happen, but this is a method I would support.
As of writing, it does not work, so don't think of sending any PMs or emails about it.
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There is a group called "Tipsters". To be added to this group, you need a mod or admin to add you to it.
As part of being a member of this group, you get a new post type: "Tip"; It has a few features.
1. It has a "make public" date. Before this date, it is visible only to members, stickied to the top of lists, and no members can reply to it. If someone links to it, and the person that clicks the link is not signed in, they will get a page saying "this page will be made public on xxxxxx"
2. When it is "made public", people that are not signed in will not be able to see any information on who made the tip. They will, however, be able to see the post. Comments will also be opened. The post will also be un-stickied.
3. If the tipster wishes to edit or delete the post before it is made public, so be it.
4. Tips must be "made public" no more than say... a month... after original post.
Part of the intent here is, "everything will eventually become public", and not forever sit in obscurity.
Thoughts on the idea?