This was discussed at various places but did not seem to have its own bug so far.
Schema.org is a metadata standard used by search engines. Google, Bing and similar search engines consume Schema.org markup on web pages and use it to weigh the content better, provide rich search results, and presumably to enrich Knowledge Graph and similar semantic databases. By providing Schema.org metadata Wikipedia articles could become easier to find.
Schema.org defines various content types; some of these are highly relevant to Wikipedia, e.g. MedicalEntity and its subtypes, MedicalSignOrSymptom, Country / City, CreativeWork subtypes, Corporation...
Schema.org markup is used to annotate existing text content, not to add new, invisible content, so it's not clear how an attempt to add it to Wikimedia content should look like - a new software feature? a wikiproject? a mix of the two? Nevertheless, until we figure out, it's nice to have a central place for dicussion.