I think the Semantic Web solves a lot of this, and could solve all of it.
Some argument structuring tools using AIF - I haven't evaluated their UI's yet.
The Provenance ontology lets us assert how information was produced and how it has been evaluated.
The goal should be the ability to filter conclusions based on arbitrary epistemic standards.
In Jim Babcock's scenario, one could create their own argument structure, linking to appropriate concepts, and linking to the existing argument only where appropriate. Possibly only the conclusion. I think AIF would also allow citing any post or comment as an argument, so freeform stuff can still be connected even if it isn't automatically filterable. Other people could do the structuring and validation.