Kotlin is here to stay, it's a pleasure to code in it. The same way ObjC gave way to Swift and I also enjoy coding in it. They both are the only languages I use today for any development. I don't care about tail-call-whatever, functional-whatever or monad-whatever, I just care about a nice and clean syntax that gets out of my way to get the job done in less time. The rest will be improved by people way more intelligent than me in whom I trust, backed by two of the biggest players in the development world, Google and Apple.