* If you read the link, there is no guarantee of backwards compatibility to the current point within future releases. This is why they're still in milestones.
* Jetbrains has yet to show us that they are, themselves, committed to Kotlin by implementing something major in it.
* They won't provide a timeline for 1.0.
I love thinking about and toying with new languages, but when it comes to sitting down and doing stuff, I need to know the environment has enough commitment such that I don't have immediate code rot.
So you would use a pre-1.0 version with no guarantees of backward compatibility to implement something real? Something that a business depends on, not just something you can toss up on your GitHub page to look cool? I would fire you as soon as we tried to update to a new version and had to spend weeks fixing your now broken code.
What I mean by that is, when will it go 1.0? When will we see a major project from Jetbrains implemented in it?
Kotlin has been around for a couple of years now and Jetbrains still won't answer these questions as far as I can see[1].
[1] - http://devnet.jetbrains.com/message/5490337?tstart=0