In my humble opinion..
Scala is great for scripting, iterating, researching, and playing around with various concepts. The downside is that its not binary compatible between major versions. There are some stability issues in production as well, some exciting rabbit holes of error stacks.
Java is like herpes. Its everywhere and is not likely to ever be gone completely. It is also rock-solid stable in production. The biggest cost is that you have to write it in Java. If only it was like scripting in Python, then this would be a great language. Incidentally Jython is not great for other reasons, but thats neither here nor there.