As we reported last week, Google began sending notifications via Google Search Console to non-news sites about getting their pages ready for AMP. Now, for sites that are ready for AMP but are not news, they are getting notifications that they can preview their pages with AMP in the AMP Demo.
The email subject says "preview AMP presence for" your site and adds, "Google has detected that your site has AMP pages that may start appearing in Google search results soon. We invite you to preview the public experience using the AMP Developer Preview site. Follow the AMP Guidelines if you wish to change or fix your pages prior to the launch."
Here is a screen shot from Alan Bleiweiss who posted this on Twitter:
Forum discussion at Twitter.