Google is working to separate its mobile and desktop search indexes, making mobile the primary index for all search engine queries going forward.
While a separate desktop index will be maintained, it will not be kept as up to date as the mobile version.
The change will happen with the next few months, according to Search Engine Land, based on a keynote speech given by Google webmaster trends analyst Gary Illyes at the Pubcon event in Las Vegas.
There's been no official announcement from Google itself, however, and the exact details of how the move will work are still unclear.
Nevertheless, it seems like the logical conclusion of Google's recent moves in search, which have been moving more and more towards mobile as the primary device for search, starting with the so-called 'Mobilegeddon' update last year which introduced 'mobile-friendliness' as a ranking signal, an effect which was increased with a further update this May, and through the introduction of AMP (Accelerated Mobile Pages) last October.