I worked on Longhorn. There were two things I remember that led to the delay: - Trying to make every component of the OS describable in a manifest, such that y

I worked on Longhorn. There were two things I remember that led to the delay: - Trying to make every component of the OS describable in a manifest, such that you could change/update/remove it on the fly. They seem to have gotten there finally in Windows 10. - Trying to rewrite all the native code in C#. Some components got there (including mine), but rewriting all of these libraries and applications at once made the OS so slow that we got to a point where it was unusable and had to take a partial reset.