He contradicts his core assertion (OS models are too complex and layered) with his first "new" feature.
Nearly everything on this manifesto has been done before, done well, and many of his gripes are completely possible in most modern OS's. The article just ignores all of the corner cases and conflicts and trade-offs.
Truly understanding the technology is required to develop useful and usable interfaces.
I've witnessed hundreds of times as designers hand off beautiful patterns and workflows that can't ever be implemented as designed. The devil is in the details.
One of the reasons Windows succeeded for so long is that it enabled people to do a common set of activities with minimal training and maximizing reuse of as few common patterns as possible.
Having worked in and on Visual Studio, it's a great example of what happens when you build an interface that allows the user to do anything, and the developer to add anything. Immensely powerful, but 95% of the functionality is rarely if ever used, training is difficult because of the breadth and pace of change, and discovery is impossible.