Without wishing to disparage the article at all (I really love this kind of article, including this specific one) ...

I feel like Kotlin is almost exactly the wrong language in this space. You either go all the way to a more powerfully typed language where Scala has grabbed mindshare, or you go fully towards dynamic languages like Python or (my favorite, even though it has almost no mindshare in this space), Groovy. It really feels like all Kotlin did here was add verbosity and cloud the actual question being answered with more syntax.