I'm just curious where the Kotlin action is happening within IntelliJ Community Edition (if any). Is there a particular branch (or several)? It doesn't seem to occupy a significant percentage of the project as yet. Thanks for the clarification!
It's happening slowly, and the main reason is that Kotlin itself depends on IntelliJ for its infrastructure and we hit the second (meta) level of bootstrapping here. We are working on updating the build sequence and all related procedures to ensure that change in IntelliJ source will not break Kotlin compiler in the way that you cannot compile IntelliJ anymore and cannot fix Kotlin compiler. For continuous integration builds this is not a big deal, since you can always use some tagged previous version, but many of IntelliJ developers are actually running a version of IDEA built from source on their own machine. There are some other issues we are facing, like Kotlin performance in presence of huge amount of Java source code, incremental compilation issues for extremely large projects and some other like this. Most of these issues are not seen in other projects, and we have quite a few internal projects using Kotlin almost 100%. Hopefully pretty soon we will see much more Kotlin code in IntelliJ project as well.
Thanks for the details - it is really good to know that development is moving forward, even if slowly. Also, thanks for implicitly improving my github-fu :).