Pointer to article:
It’s very likely that Microsoft eventually support all principal “Longhorn” technologies--“Avalon,” WinFS, “Indigo,” and WinFX APIs--on its most recent “legacy” OSs: WinXP and WinSvr2003. If and when that comes to pass, Microsoft will have taken the next big step in the direction of pure OS virtualization. When you abstract the external interface from the internal implementation of any functionality, you’ve virtualized that functionality. If all “Longhorn” external interfaces have been abstracted from the underlying kernel implementations on which they run (WinXP kernel, Win2003 kernel, “Longhorn” kernel etc.), then “Longhorn” is not a traditional OS anymore. It becomes a set of virtualization technologies that bridge the legacy Windows to the future Windows. And which, conceivably, through open source implementations such as Mono, can bridge the Windows and Linux worlds.
At that point, Microsoft will have a harder time convincing users to upgrade to the “Longhorn” kernel, if they can get the same functionality by simply retrofitting their existing OS. Virtualization breaks the upgrade cycle upon which platform and application software vendors’ licensing revenues greatly depend.