So to follow up here, there are some changes incoming in the regards to the way downstream events are propagated. We are now able to satisfy the constraint of 1.03 even if the DispatchQueue is concurrent or the OperationQueue is not a restriction of maxConcurrentOperations of 1, or for that matter any valid scheduler being concurrent; we will always send serialized events on that requested scheduler for .receive(on:). The one remaining caveat that we deviate from the specification slightly is that upstream events such as cancel() and request(_:) in our world can happen concurrently. That being said we do handle them in a thread safe manner.
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