Thought about it. I've heard a lot about Scala's learning curve, but I don't think it'd be a huge problem in my case since I already know Haskell. I
am a little worried about finding Scala programmers, but there's a decent-sized community around the language. And it can use Java libraries fine, and you can write native Scala code for Apache Spark.
The deciding factor against it, for me, is that Java/anything interop on the JVM is quite easy, but Scala/anything interop is hard. That makes it relatively easy to create a mixed-language Java/Jython system or Java/Clojure system, or even Java/Jython/Clojure, but very hard to do a Scala/Jython system. And even with its advanced features, I doubt that Scala beats Python for quick & dirty prototyping. I've got a bunch of past experience in multi-language scripting + compiled core systems, and I know the benefits of doing a system at scale like that. The value proposition of Scala (and to some extent Go and Haskell) is that you get one language that is both fast and concise, but in my experience you want to separate that out into scripting and core languages, because the styles of programming themselves are very different.