Regarding boxing: Kotlin compiler performs various optimizations to avoid redundant boxing / unboxing both before and after inlining. Basicly, if you don't use a boxed primitive in a way that would require an object, compiler shoud generate code without boxing/unboxing. If it doesn't, but you think it should, please, don't hesitate to report an issue (https://youtrack.jetbrains.com/issues; Type: Performance Problem; Subsystems: Back-end. JVM).
I'm super glad to hear that Jake Wharton has joined Google and will be improving Kotlin tooling. I'm now more motivated to learn Kotlin.