I haven't been following along too closely… but my impression is that a lot of the churn on this design review is over some questions engineers have about the implementation details and behaviors of the Sequence type itself. Since the design review implies that we ship with this Sequence type implementation… we are then ending up in a place where we potentially block the design review on an implementation review.
What if the Sequence was injectable? What if a product engineer that needed to make use of Observed Values made their own decision about the implementation of that Sequence? I do realize that could mean rethinking the original design… but it might also generalize the intended design to an extent that we no longer block a design review on an implementation review.