I have considered this as well. Others have done this. The decision to do something like that does not preclude duplicate postings, public and private. Duplicate postings are actually easier than tagging (copy, paste).
Their is a real risk of confusion, where did I post that comment? My thought was that if I did something like that I would limit it to tribe updates, Monday Mugs, FBF, etc. stays with the thread and set the ground rules for everyone to try and stay to that topic in an effort to keep it from spinning away from everyone again.
It would by its nature be exclusive. I'm not sure if this is right way to go or not.