According to Google’s Johan Muller, Google Search Console will send FYIs to the sites which are moving from the desktop-first index to the mobile-first index, as said by him at SMX Munich. In his keynote speech, he made it clear that Google Search Console’s next planned steps is to send FYIs messages in Search Console when switching.
Simon Grisser twitted in German, which has been translated to English as “Google will inform via search console when a website switches to Mobile First Index is being reset”, says John Muller.
Here is a tweet of Simon Grisser
Google never had the planning to notify webmasters of when their sites switched over, but the only intention is to communicate issues while moving to the mobile-first index. Though Google had given earlier some tips on how to notice the signs that your site has been moved, but this message would further clarify SEOs and webmasters about switching.
See the forum discussion at Twitter.