Microsoft has recently proposed the idea of automatically submitting content changes to the Bing Webmaster API to Wordpress, see #52900 (Instantly index WordPress web sites content in Search Engines) – WordPress Trac. Their end goal is to set a new standard for the way webcrawlers work, not only for Bing, but also for other search engines.
Perhaps this would be a nice feature or plugin to have for Discourse. That way forum posts would instantly get indexed by, in this case, Bing and changes would be instantly visible to the search engine.