Hey! Ya, that would be nice to support a native Kotlin library, but we don't have an official Kotlin client library planned for right now. I can say that we have Kotlin users who are successfully using the Java client library.
If you end up building a Kotlin client library and want to open-source it, please feel free to open up a PR here with a link to it.
https://github.com/authzed/awesome-spicedb