Lol, you are laughably bad to think that java is legacy.

The JVM is improving with never before seen speed, has state of the art GCs, a very good JIT compiler, upcoming green threads that will make blocking code automagically unblocking and once Valhalla hits with value types, there really will be very few areas where java would not be applicable.

And on top of that, there is also Graal, which is a novel way to run and optimize mixed-language code bases.