I'm quite interested in this data structure, but I'm not sure it applies well to Swift's Async Sequences. A big reason for this is handling cancellation, and also the way Swift's Tasks suspend and resume mean it's not quite a 1-1 mapping afaict, and atomics based algorithms aren't the easiest (understatement) to adapt.
However, I do have some ideas about using Swift Atomics at some point to create a data structure which I hope might be useful as the basis in the future for something in this area though.