thanks! I am also excited about async iterators. Back pressure is a very interesting point. Thinking about it from a nodejs perspective, node streams already handle back pressure. Every call to iterator.next will cause reading from the stream, which should trigger flow of information. If the stream/observable constructs you are using don't have back pressure built in, I would probably wrap them with a construct that has back pressure support and let generators interact with that instead. Buffering certainly has it's own limitations if you can't really pause the data provider (stream/observable). Rxjs has some good information on how it handles back pressure for its observables. http://reactivex.io/documentation/operators/backpressure.htm.... If worse comes to worse, add logic for buffering in the generator itself.

Definitely something I have been pondering and to consider when dealing with async iterators that interact with data providers with no back pressure handling built in.