Kotlin is not just for android apps.

Kotlin is getting first class support on next generation Spring web framework with functional programming support - https://speakerdeck.com/sdeleuze/functional-web-applications...

it's almost done with first class support for vert.x which is a high-performance reactive webframework https://github.com/vert-x3/vertx-kotlin-common

The reactor project (erlang for the jvm?) is building first class support for kotlin https://github.com/reactor

I think its going to be a great year for building backend systems on jvm.