Unfortunately, what Java really does isn't only to be that combination of low-level and high-level. Just as vitally, (1) it is nice and easy and familiar for programmers familiar with current mainstream languages -- C-family syntax, approximately the usual control structures, few concepts that someone who's already programmed in C or C++ or C# or whatever won't find reasonably familiar -- and (2) it comes with a big bag of libraries for doing standard things: UI, database connectivity, regular expressions, logging, XML processing, and so forth.

Yes, ML is pretty good at those underlying principles; yes, you can use it to write code that's compact, safe, and fast; but it's not going to replace Java because #1 and #2 make Java easy for "ordinary programmers" doing ordinary businessy programming in a way that ML isn't and probably never will be.

(For the avoidance of doubt, I am not arguing that anyone who is comfortable in ML should use Java instead.)