Go was the other serious candidate, but it just hasn't been implemented in as many Production systems yet, and the best Go engineers I've known have been hackers, whereas we're building a robust analytics platform that requires more caution. Type safety is easily added with TypeScript, and NPM is awesomely handy.
For what it's worth, we're using go at k6 as the backbone of our tool. From what I can tell, we've yet to regret that decision. Would be awesome to hear your thoughts in a year or so, when you might have noticed the potential tradeoffs in terms of performance. 👍🏻