I'm sure there's some reason this isn't the answer, but haven't we had ngen since time immemorial? Aren't all of the assemblies that get shipped with Windows actually compiled to the native architecture?

NGen is more like a cached result of the JIT output. It was never particularly fast, and in some cases actually worse than normal JIT. The main benefit you gained from it was assembly load times.

And it most certainly didn't do anything about the dependencies on the runtime (VM, GC etc).