It's ready when it's ready. There's no time commitment from JetBrains.

It is usable now even for production although the compiler is not yet optimized and the language is still evolving.

these are latest updates

http://blog.jetbrains.com/kotlin/2013/06/kotlin-m5-3-idea-13...

http://blog.jetbrains.com/kotlin/2013/04/kotlin-m5-2-intelli...