Kotlin is pretty cool generally, but I'm not so sure it would help the problems of Android development that much, since most of your time will be spent dealing with the plain-Java Android classes and how Android expects you to do things. You'd have to rearchitect the whole Android system in it to really make a difference, and if you're doing that already, it probably doesn't matter that much what language you're doing it in.
I hope Google gives Kotlin 1st class support in android studio and even pushes it as the default language as it is more pleasant to use in my experience.
Not sure single file creation of an Android app (with a user inferface) is possible/advisable though since the separation of view concerns and logic concerns can come in handy. Gradle can be confusing to a first time user but Android studio does provide a GUI for managing dependencies.