Still lots of kotlin-features I don't see land in java soon. My favorite is passing a lambda in brackets when it's the last argument to a function. Makes it easy to make semi-dsls and nice-looking code. So instead of

  myFun(someVar, { it.something() }) 

it can be written like

  myFun(someVar) {
    it.something()
  }

or if no parameters to the function other than the lambda like

  myFun {
   it.something()
  } 

making the function almost look and behave like a language keyword. I also use extension-functions a lot. Especially for libraries or legacy-java code we wont touch. Where I work we now use Kotlin for all new backend code. And we don't do any Android.