Both ZDNet and Verge are reporting that Microsoft is building and trialling something called "Windows 8.1 with Bing." Sources say that this version of the OS will be bundled with "key Microsoft apps and services"—and be free to upgrade, or at least very, very low cost. The reports suggest that the Bing-centric version of Windows 8.1 may even be offered to PC makers, in a bid to offer a lower license price point, making cheaper devices more affordable.
Essentially, you'd be looking at a version of Windows 8.1 literally dripping with Bing. Bing as every turn. Bing, Bing, Bing. Bing? Bingo! It's not so much that the OS would be ad-supported, more that every thing you do would be through a prism of Microsoft's search and, in turn, ads. That would means that you wouldn't see any more promotional content, but you'd be served the ads that Microsoft wanted you to see—as opposed, to say, the ones you'd see if you were using exclusively Google products.
Of course, even if Microsoft is working on a project like this, it's not clear that it will ever make it out of the research lab. But if it were to, it might not be the worst thing ever—with ads no more explicit than a usual computing experience, offering yourself up to Bing could be worth it. Just. Maybe. [ZDNet and Verge]