Ask HN: Diversifying knowledge portfolio as a web dev?

I am a full stack web developer with 6+ years of experience, mostly doing Ruby/Rails. I also know some Clojure but have been using it for fun side projects only. Talking about securing my future as a developer, it looks to me, like there are a lot of highly paid jobs for Scala developers and that Scala has been progressing for the past few years. Also, Go looks like the next standard de facto for highly loaded web APIs and is also quite well paid. As for more abstract things, data collecting and processing fields also look promising, even in our small startup we have business intelligence team doing Data Mining. Seems to me like it's the future for many companies also. What are your thoughts? How do you decide what to learn next?