Back in November, Google began noting whether a website is mobile friendly in the search results themselves. Now, just five months later, Bing announced they will be doing the same.
This news came almost simultaneously with a report that queries including "near me" have nearly doubled in the past year, with 80% of "near me" searches coming from users on mobile devices. This suggests that as a result of smartphone penetration, search engine users are ready to buy right now more than they have ever been before.
Thus, we can expect Bing will take more steps toward favoring mobile-friendly websites.