Like API server objects? In theory, you could use any language for that, but if you mean to knock Golang off its throne as the de-facto k8s programming language, that's going to be difficult, and not entirely up to JetBrains.
Golang has a few things going for it that has made it very popular in the k8s space. #1: It's easy to understand and write idiomatic and performant code. #2: It's easy to create and distribute CLI tools, since you can cross-compile for all of the desktop platforms on a build server (Linux). #3: Good and easy to understand thread management. (Plus, other things, I'm sure.)
Kotlin probably has #1 and #3, but not #2, as far as I know.
Plus, Golang has a lot of momentum by now, which is going to be very difficult to catch up with.