...is that Nadella is planning on dumping Ballmers "devices and services" push that tried to expand Gates' old "Windows Everywhere" strategy into the handheld and online world. Nadella is very much a mobile and cloud guy, and the chatter is that he wants to re-engineer the company to focus on that.
Windows, Office, and their other platforms may get spun off into a subsidiary, or at least into a secondary division. Same with Microsoft's gaming division. Their less profitable non-mobile products may be eliminated completely (keyboards and mice? Skype?) I know a few MS employees, and they're all freaked out about the possibility of massive layoffs.
Of course, you have to take it all with a grain of salt. Anyone who has ever worked at a large company knows that, once "shakeup" rumors start, they can get pretty imaginative (and there is apparently one rumor running around MS that most of the American employees will be laid off and development will be shifted to India). In this case, because Nadella has made no secret of the fact that he doesn't like Microsoft's structure and direction, I think we'll probably see some fairly wide ranging changes, but I'd honestly be floored if Windows went to some sort of subsidiary. That would be a hard change for most of their shareholders to swallow.