Maybe it is better than Groovy, Scala or Jython but it is not better enough to replace Java. It has few more improvements than Groovy and that's all. Just another JVM language. We still need to fight with XML and JARs. Compilation is even longer and Gradle works slower with Kotlin. Look at Java position and Groovy or Scala position over the years in TIOBE index. Another null check or closures are not enough to make programmers change the language. And now look at Golang position. It has no generics but it's small, has short compilation time, package managing for humans and one exe deployment. This is the real language for programmers. Kotlin is just another JVM language and that's all. It has no real offer for Java programmer.