AsyncAndroid.kt

package kotlinx.coroutines.android

import rx.Observable
import rx.android.schedulers.AndroidSchedulers
import rx.schedulers.Schedulers

fun asyncAndroid(
        coroutine c: RxController<Unit>.() -> Continuation<Unit>
) {
    val controller = RxController<Unit>()
    c(controller).resume(Unit)
}

@AllowSuspendExtensions
class RxController<T> internal constructor() {
    suspend fun <V> Observable<V>.awaitSingle(x: Continuation<V>) {
        this.single()
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribeWithContinuation(x)
    }

    private fun <V> Observable<V>.subscribeWithContinuation(x: Continuation<V>) {
        subscribe(x::resume, x::resumeWithException)
    }

    operator fun handleResult(v: T, x: Continuation<Nothing>) {
        // no op
    }

    operator fun handleException(t: Throwable, x: Continuation<Nothing>) {
        // no op
    }
}

UseCase.kt

val userApiClient = UserApiClient()
val articleApiClient = ArticleApiClient()
val id = 10L

asyncAndroid {
    try {
        val user = userApiClient.get(id).awaitSingle() // other thread
        val articles = articleApiClient.getArticles(user).awaitSingle() // other thread
        binding.result.text = "completed!"  // main thread
    } catch(e: Exception) {
        binding.result.text = e.message  // main thread
    }
}