This is a pretty big idea but perhaps one of the only ways a forum has a chance to compete with the big social networks.

In the same way that WP (I think through Jetpack with Publicize?) allows the publication of posts to be broadcasted on linked social networks, could an addon be created that allows users to link their social media accounts and have it post to Facebook or Twitter each time they create a topic in the forum, or reply to another topic.

In my mind this would drive so much interest in the forum beyond the site and naturally bring in people that would be interested in the topics being discussed.