It seems to me that what is wanted is the ability for the user to
* create user-controlled custom groups, to which the user can add whomever they want
* An option to automagically maintain a user-controlled custom group of "buddies"
* create user-controlled custom profiles, in which the user can specify whichever permission they want for each group (general or custom)
* create the ability to apply custom profiles to topics, rather than to boards. topics without profiles would use the board's profiles. Permission on any topic would be the most restrictive of the combination of board and topic permission. This will be tricky, combining all those A's, D's, and X's properly for people who are in multiple groups, where they might have A, D, and X permission on the same pouvoir.
SMF 2.0's interface for groups would work OK, but you would only want the current permissions profile interface available as "advanced permission setting" option. You'd want a dead simple interfact that allows them to choose only "groups which can see this post", or whichever set of options you want to present, but then passes that information to a method that then either creates a proper permission profile, or else re-uses one of the standard permission profiles (which must be provided, and you cannot allow ADMIN to delete them, or else the whole thing breaks).