JVM dependencies in the domain layer?

One of my motivations for clean architecture is to have a use case / entity that is prepared for cross platform deployment. I'd like to eventually be able to use Kotlin to either deploy use-cases to a React Native like app using Kotlin/JS, a typical Android app with Kotlin/JVM, or typical iOS using Kotlin/Native.

That means use case / entity can not only be absent of Android dependencies, but JVM dependencies also. Therefore no RxJava to lean on for threading and Observable reactive api.

Is anyone else thinking about this problem and come up with a good pattern for connecting the Observable in the data layer to the Subscriber in the UI when there's no RxJava in the domain?

Or do you think going this far with clean arch (avoiding jvm dependencies) is premature?