Scala has been around longer, sure--but it's also
a bunch of stuff that doesn't really work well together and I'm still not sure that most (not all, by any stretch) Scala programmers really know how to write a program in Scala that's there to be maintained over the long haul. It can be done, but the pull of the super-broad feature set seems so strong that most of the developers I know personally,
including me, write code that's awful to read two months down the line because it's dense and featureful and so very
clever (note: very, very pejorative; the line about needing to be twice as smart to debug code as you need to be to write it applies here).
Kotlin is literally Java plus sugar. That's all it is. It encourages doing the right thing through stuff you could totally do in Java but nobody does because it's awful to write in Java. And, TBH, for the 90% case that's pretty great. There's no Shapeless in Kotlin--but that's a good thing, because Shapeless encourages developers with skill but no taste to do awful things and inflict them on, say, me. ;)
So, no, Kotlin's not experimental. Because experimental is a mindset, not an alpha/beta release stage.