Well, it is broadly used by Android developers. For me Kotlin is above scala just because the tooling support (JetBrains the main developers of kotlin), and I find a big difference when writting kotlin and scala. I feel scala more difficult to read, while kotlin is just a pleasure to read code. Moreover you can mix java and kotlin in the same project without issues.
I don't mean to say it will be behind Scala, I just mean to say that it will end up in the same situation as Scala, a language that was meant to be a "better Java" but could never gain enough traction to take off.
When I used Scala I never though it would be better than java, just another alternative. But I think kotlin is better than java. I hope it gains traction but not sure about it.
Why do you think it will be behind scala?