delayUntil.kt

fun <T> Observable<T>.delayUntil(value: T): Observable<T> {
    val replaySubject = ReplaySubject.create<T>()

    val sharedObservable = this.publish().autoConnect(2)
    sharedObservable.subscribe(replaySubject)

    val delayObservable = sharedObservable
            .first { it == value }
            .concatWith(Observable.error(IllegalArgumentException()))

    return replaySubject.delaySubscription(delayObservable)
}