This is an interesting idea - in effect the “flag” permission/trust level could include a pre-screening method.
Why not go ahead and display the post (without a click) with a special color/format (grey on grey) only to users of the “flagging” trust level, indicating that it hasn’t been approved, and provide a single click to approve or flag it. That’s what you’re really looking for - a pass/fail snap-judgement. Like with flagging, keep a count of “approved” and when the threshold is reached, it becomes a full fledged post.
I’m not sure how this would interact with the new posts indicators, though… And there are probably other side effects.