Private Messaging
Sometimes when in a thread, you find yourself discussing subjects that are not relevant to the topic or the comments section broke on you and it's becoming difficult to continue the conversation that no one else is in on anyways.
We get private chat rooms in the client, but it can be an inconvenience to have to find each other like that every time you want a private discussion, and sharing emails is a more personal method of communication that I'm sure few actually practice...
So how about a private messaging system?
Obviously, the report system absolutely must be available, maybe even have a priority system for it because dealing with a person's behavior by yourself is more difficult than in a thread viewed by multiple people capable of reporting.