XAML-only workflows have been around for years, but are only now becoming popular. At SplendidCRM, we started using XAML-only workflows as the basis of our workflow engine back in 2008. The big benefit is that a non-programmer can create a workflow using our online tool. We then load the workflow as necessary and run it. It is very cool stuff.
The problem with all your requests is that, if fulfilled, the system would be about as usable as Linux is as a Desktop. I manage one SUSE Linux box, so I'm speaking from experience, though limited.
Although your requests sound reasonable, the end result would likely be as bad as the Vista security model. Yeah, it sounded good on paper, but the reality is exactly as depected in the Apple ad.
I don't use Vista. Instead, I develop directly on Windows Server 2003.