Smalltalk used to be an OS, and there have been some things resembling ports of the Smalltalk image to JavaScript. Also, JIT compilation is good enough, that such an OS need not be a dog, provided a clean architecture. BeOS showed that to be the case on machines orders of magnitude slower than today's.
BeOS was written in C++ and compiled with gcc 2. For all intends and purposes the whole operating system was native code, certainly not running over a VM.
Yes, but it could achieve feats of multitasking and multimedia display mainstream OS could only achieve on machines with much more power. It showed that a 10X increase in efficiency is possible though architecture.
