as the spec does not explicitly mention it, can you please confirm that what the spec actually wants to say is that CompletionStage does not only imply async when declared as a method's return type, but also when CompletionStage is de-facto returned by a method or by a interceptor (i. e. the method itself is not declared to return CompletionStage, but might return Object and an interceptor produces a CompletionStage from that)? This would allow framework providers to provide "JAX-RS adapter" like an interceptor turning RxJava's Observable into Java 8's CompletionStage. The spec is a bit short here.
