Kotlin uses the same VM and API, so it makes no difference in this regard. It's not a big change – it's fully interoperable with Java. You can easily take a single class in a Java application and rewrite it in Kotlin, and everything continues working just as before.
Google adopted it because, as they more or less said in the announcement, it was already being adopted by the community and it hugely improved development experience.
but you splitting your developer base.
* There will be people better at kotlin
* There will be people better at java.
This is a problem when you are looking at hiring new people etc . This fragmentation is going cause issues just because people are hedging against Oracle future decisions.
In a perfect world Google should have bought Sun and the current version of Java would look at lot like Kotlin.
Kotlin is a light syntax for a coding style. It's as easy for a Java dev to learn Kotlin as it is to learn Spring or Hibernate or whatever library or framework the team at your new job uses
Google adopted it because, as they more or less said in the announcement, it was already being adopted by the community and it hugely improved development experience.