Longhorn is a bit of a moving target, yet Microsoft maintains any and all drivers must be built on the .NET framework for Longhorn.
It is the sole reason ATI has already converted the Catalyst Control Center to use the .NET framework.
However, the original design docs of Longhorn does not resemble much of what is really going to be Longhorn at this time. A bit speculation could be made which says Microsoft will not go with the .NET framework for the underlying architecture of Longhorn, but it would be pure speculation at this point.
