Nice to know about this, thanks for the post, Sarah. A base needed to be native! To my eyes this could represent a de-facto statement from Google about the deep reach of WordPress within WWW, to some people including me this is more significant and engaging than the promo phrase “running 25% of the WWW”. In other words: “WP is a big part of the WWW, we want to crawl it better”. I buy that. Sitemaps are not that top story they used to be years ago, but still represent a real time inventory of URLs, thus a primary tool for any webmaster or SEO related work. I am curious for what’s next, with developers releasing brilliant side-functionalities from this new XML sitemaps in WordPress core. Thanks to all those involved, not only for this particular development.