It is also still much slower than Groovy and Scala, being at the same time similarly or even less expressive and having worse tooling. Therefore I can't see any

It is also still much slower than Groovy and Scala, being at the same time similarly or even less expressive and having worse tooling. Therefore I can't see any reason to move from e.g. Java to Ruby. When Java is not expressive enough I'd consider using Groovy/Scala/Clojure.