Just think a micro kernel OS, most services is implemented as a standalone process, not in the kernel itself.
Also, I think the JVM can only provide such a micro kernel, and defines the interfaces and specification, and we may implements a new GC using Java, a new JIT using Java, a new Memory using Java and etc. Since all the code runs in a union memory address, there will be less cost on communitions than OS level messages. I dont think the speed of Harmony will bet Hotspot in 1 years, But i hope it will bet Hotspot after 1 or 2 years, So i dont think using Java to implements it, and using a micro kernel architecture will be a problem.
