For me this question should be rephrased “What language for writing OS we need?” and this is rather question to OS community, not to Julia community. Speed is only one factor among many, important one, but probably not the most important. What I mean about that, Android is written in Java, because convenience of using it outperformed loss of performance on smartphones.
From what I see, OS writers prefers rigid, explicit languages and one of the most problems with C is that it is not rigid and explicit enough. Yes, in C you need to declare types explicit, and from what I understand, this is what OS people want. You must stay what a type of variable is to everyone to know. Problem is that you have implicite conversion in C, so this knowledge is “lost” for programmer at some point. Go language, which was never aiming for OS writing, but for servers, removes implicit types conversions for all types like ints and floats, there only exception when it is allowed are some wrappers of previous types. I believe Rust did similar things.
Needless to say, this is opposite of what Julia do. Maybe not on the real of type conversion, but implicit calling of type specialized method. In Go you can’t write intVar + intFloat, because in Go don’t allow implicit conversion and has no notion of adding int to float. In Julia + can have literally hundreds of meanings and you can add another one itself. It take from us a much of burden of thinking about types, but while it is liberating when making numerical computation (and many other things), it seems be a opposite of what most OS people want.