During the SMX Munich John Muller from google revealed a few new pieces of information about their mobile first index.
Google will be notifying site owners when their site has been moved to their mobile first index.
Google has started moving approved sites to the new index. Google is working on contacting the site owners when the new index has been put in place for their website but so far no one has been contacted as of yet.
There is one main way to check if your site has moved to the new index and that is by checking your sites desktop traffic and see if it has dropped a bit compared to mobile visits.
John Muller said that the mark up on your mobile site will be important in the future as google may not be referencing your desktop version as a website.
If you are looking to build a new mobile website then contact Simply Digital