Read other letters about this article
Give the writer/readers a topic for each month. See www.witchvox.com for an example of how this works, although that is most of their content, rather than a news website.
Question - do the writer/readers own their own content or does it become the property of Salon.com by virtue of being published there?
Pay the writer/readers a tiny honorarium or some other compensation through a page view or other rating system, or facilitate a voluntary pay pal donation system for the writer/readers.
Use a visual map of the general topics covered by the writer/readers to allow a way to see the whole picture and how the topics link together. See Etsy.com for an example of how this works, use the search by color or one of the other visual maps of the content on the site.