Who would have thought that a brand new language wouldn't have the features, library support and optimization that the more popular languages have? Should be obvious, but then you read through HN posts with people dismissing languages like C++ and Java as 'too old' or something and that you need to use some brand new untested language to be worth talking about.

Never select a language based off hearing about it on HN or blogs. Either stick with what you know or use a tool that has very specific optimizations for the problem you're going to tackle (and no, concurrency is not a good option to jump off the JVM as it has incredible concurrency support already: see https://github.com/LMAX-Exchange/disruptor for the fastest concurrent bus I've seen in any language). Of course, there is nothing wrong with testing out golang or haskell - just don't force your paying client to test it out with you or you might be one less client shortly.