At SMX this week, Gary Illyes dropped a bombshell when he stated that Google is working on a mobile only version of the search index, which would see desktop and mobile have completely separate search indexes.

Not only is it in the works, but Google currently has a team working on this, which definitely means this has gone well beyond the “well, this would be a cool idea” stage.

What would having two indexes mean for webmasters?  It definitely does raise the question about whether webmasters should be focusing on the user experience for both desktop and mobile as completely separate user experiences.  So while Google has recommended responsive design for quite some time, it would seem responsive might not be the best option if SEOs would need to focus SEO and potentially different SEO tactics for ranking in two different indexes.

If you are still working on changing your site over to mobile before the April 21st date when Google turns on the mobile-friendliness as a ranking signal, it is worth considering which style of a mobile site you implement, whether it is an m.example.com site or a responsive which is essentially the same as desktop, just designed so it scales appropriately on a smart phone or tablet.

So just how far along is Google in working on this?  Gary Illyes says that while they do have plans to do this, he is not sure what stage they are at.  And unfortunately, they have nothing to announce about it.

There is full coverage on Gary lllyes comments about mobile here.