As you may know, Google began rolling out the mobile first indexing process a few weeks ago, although, I have yet to see anyone report they believe they are now being crawled in a mobile-first way - nor did anyone yet get Search Console notifications of such. That is for another story...
What surprises me is that Google has said time and time again that how Google decides when to move a site to the mobile-first indexing process is based on if a site is technically ready for it or not. However, a new theory I spotted this morning, which was debunked by Google's John Mueller said that Google moved sites to this new mobile-first indexing process based on search volume.
Martin MacDonald asked John Mueller "MFI will be triggered depending on the share of mobile vs desktop queries that a site is returned by, right? Ie. if you get *high mobile search volume*, then, MFI?" John Mueller immediately said "nope."
Nope.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) April 18, 2018
John then went on to explain it has nothing to do with search volume but rather a simple and straight forward technical change. If your site and pages are technically ready for mobile-first indexing, i.e. the mobile and desktop pages are equivalent, then you are ready.
There's nothing to elaborate - afaik we never mentioned that, so I assume you're being creative and making things up. It's good to see creative SEOs, but this is a pretty straight-forward technical change.
— John ☆.o(≧▽≦)o.☆ (@JohnMu) April 19, 2018
Forum discussion at Twitter.