Does anyone know of a solution out there to enable (at the category level) some protection to not only disallow lower trust levels from replaying to topics, but also from seeing replies?
I have a category with some wikis, and I would like for the “staff” to be able to have discussions, but only have the main post itself be visible to non-staff members.
Not a category-specific solution, but have you looked at enabling whispers? That sounds like it would address the issue of having staff-only discussion within the post, particularly if all your wikis are in a category where non-staff members can view but not reply.
This seems like a viable solution. Although, if it were possible to require replies to be whispers that would be even more awesome.
Thanks @BenLeong. 
Perhaps if you set the permissions to read only. That wouldn’t keep admins from being able to reply, but I think it would for other staff.