Yes! Another project makes it off the back-burner.
After a recent discussion on Meatball wiki, I dug out an old half-finished project : Typed Threaded Discussion, and knocked out a basic working sketch.
Typed Threaded Discussion allows a community who want to argue in a productive way, to do a minimal amount of mark-up that captures some genuinely valuable structural information. The forum is just a basic threaded discussion group with the twist that users categorize their posts according to the relationship to the parent; whether it's a counter-argument, offers supporting evidence, asks for clarification etc. The tree of threads is then presented sorted by type. And the result is a navigable map of the relationships between the points made in the discussion.
That's the idea anyway. Now I need to test it, to see whether the results are interestingly different from normal threaded discussion. Volunteer testers welcome.
Try it out here.