[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]

Ghosting will only result in a loss of what the PM was meant to be: A place to trust that messages may be sent to other members without fear of anyone else seeing them.