Baseline compilation is fine, that wasn't what I was referring to. I the context of this thread, the long-awaited promise of JIT is the ability to profile running code to dynamically determine the hot portions and re-optimize on the fly, and do this continually for the entire runtime of the program. This is what people mean by "things that are impossible for a static compiler to do" (though PGO is a decent approximation), and the basis of all discussions that begin with "actually, Java can be faster than C". This is not to say that Julia does not satisfy the definition of a JIT, only that using Julia as an example of this principle appears to be mistaken. Julia is not fast because it dynamically re-optimizes, it's fast because it uses a mature C compiler backend.
Going straight to machine code via baseline compilation is a common JIT technique. Until a couple of years ago, V8 compiled everything.