Microsoft has been working to detangle the Windows hairball since it was developing Windows Vista, and possibly before. MinWin is the Windows "core" that resulted. MinWin includes some kernel interfaces, but it isn't simply the Windows kernel. As I've described it in the past, MinWin is the heart of Windows, organized in a way so that none of the included parts has any dependencies on anything outside of MinWin.
So what is MinKernel in this context? According to one of my sources, MinKernel is a minimal set of functionality that is shared across the different Windows kernels that run on x86, ARM, Windows Phone and Xbox. MinKernel is the one base-level implementation on top of which these platforms are built, the same way that BaseFS may be the base-level file system that is common across different platforms.
Villinger also found a few more Blue clues worth noting. He discovered some references within the Blue bits to a Modern/Windows Store version of the Windows Defender antivirus app that Microsoft bundled with Windows 8 and Windows RT. (Right now, Defender is a Desktop, not a Metro-Style app.) He also found some hints that indicate that 3G/4G tethering support may be built into Blue.