Hello.
I've been watching Kotlin development for a long time and at this moment I really think it is the best static-typed programming language on top of jvm.
One factor that stops me from investing more time in using it is that it is still has 'in development' status and the time it will be 'production ready' is unknown. This is connected with several bad thoughts, such as:
1. What if the language will be 'prod ready' only in 2-3 years? Whole ecosystem can change till that time, Kotlin grammar can change, standard libraries API can change, incompatibility might appear, etc.
2. In 2014 Java 8 will be released. Even right now it is hard to change java for something else (excellent IDE support, lingua franca for most of JVM devs, existing frameworks compatibility, confidence in future), but after java 8 it will be even harder - some of the features (lambda + compatible with it collections api) will appear in java.
It means that even if someone have the urge to get some convenient functional programming features in language (lambdas + collection's api), this urge will be somewhat satisfied with Java 8. Scala has already gained significant (for alternative language) momentum for advanced developers (moreover, Scala has growing number of developers thanks to EPFL students), java will become less crippled safe bet, and Kotlin won't have a niche. If it will happen, it will be more safe to stay with Java and Scala because of the confidence in their future support.
To summarize, I think it is necessary to announce the date of the final release and to start polishing compiler, existing features, tools, make usable plugin for eclipse (personally - hate this IDE, but there are many who finds something adorable in it).
1. If you are starting new project, I think Kotlin is a great choice already, especially for the Android environment.
2. I've kept track of the Kotlin programming language evoluation for the past 12 months and so far the team has been thoughful in discarding/adding features.
3. Since Kotlin has high compatibility with Java already (not sure if the 100% mark has been achieved), Java 8 is not a threat. You can start your project in Kotlin and utilize existing Java ecosystem without compromise.
4. Scala was introduced almost 10 years ago. It make sense that it has a bigger mindshare over Kotlin which is not released yet. But I think Kotlin fits nicely between Java and Scala. For Android mobile development, Kotlin by far is the best language for it.
5. The great thing about Kotlin is that you don't have to be an 'advanced developer' to pick it up. It is quite easy for beginner developer to adopt and get the benefits.
6. I like the current approach of maturing the language, completing the toolchain and improving the performance. Let's call it production ready when it is actually ready instead of picking up an abritrary date in the future. You only get to call version 1.0 once :)
start polishing compiler, existing features, tools, make usable plugin for eclipse
Documentation. Documentation, documentation, documentation. I know this will sound like a cliché, but the most important thing that Kotlin needs right now is proper documentation. Which means: a complete specification and a set of tutorials, both of them of course up to date. Look how Dart is doing it -- they have pretty awesome docs.