I think the important contribution of Meijer and RX is realizing the duality of IEnumerable and IObservable which enabled them to use the same programming constructs. The meat of RX is in all the combinators so you can express complex behaviours very succinctly.
Hmm...Smalltalk had the same iteration methods over streams and collections since at least Smalltalk-80, so not sure what the important contribution here is.
Whether the flow is push or pull is a fairly irrelevant implementation detail for a dataflow system.
That doesn't mean it can't have big effects, but if you're relying on those, or they do become relevant, you should probably ask yourself whether your system is really dataflow.
