if (throttleTime > TimeSpan.Zero)
{
    var shared = observable.Publish()
                           .RefCount();
    if (scheduler != null)
    {
        return shared.Buffer(() => shared.Throttle(throttleTime, scheduler))
                     .Cast<IReadOnlyList<NotifyCollectionChangedEventArgs>>();
    }

    return shared.Buffer(() => shared.Throttle(throttleTime))
                 .Cast<IReadOnlyList<NotifyCollectionChangedEventArgs>>();
}

return observable.Select(x => new[] { x });