[quote=@UltikanaRe]
Idea: Can view/Can comment/Can edit/Ghost PMs:
Jack, Jill, John, and James. have a PM.
Jack starts the PM. He doesn't want Jill to know John can view the PM, so he sets John to 'Ghost'.
Jack wants James to only be able to comment on some ideas, so he sets him to 'can comment'. Comments would work like replies that appear in margins within hider-like things.
[/quote]

Please, no "Ghost" setting. That just invites further drama. I'd rather make people go through the extra step of copy/pasting PM text to someone else, to have to [i]think[/i] about the action, rather than let them choose a one-click setting to do it. If it's totally legitimate copy/paste, then fine, the person will have no problem with it. If it's to create drama, well, then perhaps the effort will make them reconsider. 

Otherwise, I like it. As long as all participants can see who can do what, I'm golden. 

Is there a 'can reply' permission? Or is that your 'can edit'?