@Eldenroot Flagrow created their own twist on "private" discussions. What @Shahiem is trying to develop is no way similar to what flagrow/byobu provides as far as concept other than privacy. He is developing what is considered the "classic" forum approach to private messaging (PM's). This concept pars fairly with bulletin board software such as Vbulletin, XenForo, PHPbb, etc.
I use Byobu for private on-board discussions and because it has it's own crazy twist that I like over the classic way (i.e. host meetings, off-chat discussions, private fanclubs, etc).
What I will use @Shahiem's extension is to provide my community with "Private Messaging" through an inbox-styled interface.
Private Discussion = / = Private Messaging System.