@Blundell Kotlin/Native already supports Zephyr thanks to @msink, and there's a sample in Kotlin/Native repo (I wish you good luck to run it on a machine, from someone who didn't try though). I'm not sure libraries can support Zephyr yet though, because it seems there's no standard preset. I know you'll not have kotlinx.coroutines on it for example, but you might be able to compile it yourself, which could be ok, but could be cumbersome if you need several third party libraries, and might lead to long compilation time.
I bet Kotlin for embedded systems is not being forgotten anytime soon and will eventually be a thing in the future, but I know JetBrains is currently focusing on other parts of Kotlin/Native, and doesn't have a team dedicated to embedded Kotlin yet.