NaCL is open source, the papers and documentation are all open, the build tools are all open. The only thing it's not is standardized -- and that's not Google's fault.
Apple and MS are vested in their platform plays, and Mozilla has been playing a comparatively weak technical game for years.
So basically it's a great solution except for the part where everybody else has misgivings about it. There are already standards covering almost everything from NaCl, and going by what it was supposedly for according to their original marketing campaign, 3D games, entirely supplanted already by current generation JS engines
It was a myopic stop-gap that's already starting to show its age, about the only thing it has left running for it is smaller distribution size and faster cold-start times, but they're implementation problems of current generation JS, rather than some fundamental benefit of NaCl
Uh, when did that happen? It's slow, it's complex, it's a terrible solution, it's barely seen any uptake and near zero interest from tool vendors.
Oh, and it's objectively, demonstrably inefficient. This is just another version of "I implemented something simple ... in JavaScript!". What lunch got eaten?
Apple and MS are vested in their platform plays, and Mozilla has been playing a comparatively weak technical game for years.