According to a site, Build Your Own Search Service (BOSS) is built on the Yahoo index as its foundation. A company can build their own search engine using Yahoo’s underlying technology and differentiate via the user experience.  Essentially, that’s what Yahoo is planning to do now with Bing as their underlying technology. No more Yahoo index likely means no more BOSS.
http://searchengineland.com/what-site-owners-web-developers-and-seos-should-know-about-the-yahoomicrosoft-deal-23344