> JVM is written in a mix of Java and C++, let me know when they start rewriting it in Kotlin.

This is less relevant today. The host blessed languages do have an advantage, but I would not say it is insurmountable. It might have been the case in the past, but the modern JVM is a platform, it is no longer a glorified Java language interpreter.

> Now a couple of places are adopting Kotlin outside Android, nice, eventually will migrate back in about 5 years time.

Maybe. Maybe not. Most developers I talked to that have experienced the transition do not want to go back to Java.

This isn't to say Java will die. It will continue to thrive. But Java dominance (on the JVM or as a whole) isn't a sure thing anymore.