You are right, much time have passed since NT 3.1. Those days microkernels was thought to be the state of art, the future of kernels. Smart people claimed that as the hardware evolve, the performance gap between monolithic kernels and microkernels will become negligible and the robustness of microkernels will make it superior.
But it did not happen. Today, monolithic kernels dominate the desktop market, the only exception is OSX with its Mach kernel. The quasi-micro NT kernel was turned into a bloated monolithic kernel, BeOS died, and Hurd... hasn't really born yet.
Conclusion: monolitic design is still the way to follow.
Now back to the original topic: I don't really see any reason for userland graphics except stability. It WILL decrease performance, which is cruical for the VGA cards, and might result in driver incompatibility I think. If I'm right, then it will take quite some time to write compatible drivers for older cards (assuming that nvidia and ati is willing to write for their own cards). And Microsoft does not have time, they already decided to leave out WinFS from Longhorn. They can't postpone Longhorn beyond 2006 because that would be too big pull for desktop Linux/BSD. And I guess by 2006 ReactOS will become a usable OS too.