I don't think that encouraging scala code is good purely for maintenance reasons. If there's a choice, it should be java. Not saying that learning a new language is not cool - but in practice people are a bit put off by maintaining Scala code. Its not only about what the writer of the code prefers as a language: it's more important what the maintainers of the code 

will has to work with.

Would such maintainers also be put off by new language features (lambdas) in Java 8 when we (eventually) baseline to it?  :-)