Given the url structure Discourse uses, Google has little hints about the hierarchy of the forum. How about adopting the microdata for breadcrumbs? Discourse already has the categories in the right order rendered in the posts page.
I don’t have any articles to indicate if ranking improves. One of the advantages is to allow the user to get to a particular category from the search results. The breadcrumbs replace the link, just bellow the title.
Implementation with microdata is trivial:
<div itemscope itemtype="http://data-vocabulary.org/Breadcrumb"> <a href="http://www.example.com/dresses" itemprop="url"> <span itemprop="title">Dresses</span> </a> › </div>
My fork points to a private repo out of Github so I don’t know how to send a pull request. Is anyone interested in implementing this?