Paul Thurrott heard rumors that Microsoft is planning to ship "Threshold" (Windows 9) in April 2015. Threshold will reportedly acknowledge that Windows 8 didn't resonate with customers and will feature Metro 2.0, a more mature version of the Metro design language used by Windows 8. It's not clear what will change but perhaps a windowed mode that works on the desktop is part of that.
Windows 9. To distance itself from the Windows 8 debacle, Microsoft is currently planning to drop the Windows 8 name and brand this next release as Windows 9. That could change, but that's the current thinking.
BUILD vision announcement. In case it's not obvious that the Sinofsky era is over, Microsoft will use BUILD to provide its first major "vision" announcement for Windows since, yes, Longhorn in 2003. Don't expect anything that grandiose, but the Windows team believes it needs to hit a happy middle ground between the KGB-style secrecy of the Sinofsky camp and the freewheeling "we can do it all" days that preceded that. As important, the firm understands that customers need something to be excited about.