This lines up with my thinking. The proposal should give us a building block in the form of the primitive. I would expect the grandparent comment’s API to be provided in a library built on top of a language level primitive.
How would you then deal with a stream of UTF8 code points? They won't fit in a UInt8Array. There will be too many for async iterators to perform well: you'll hit the promise thrashing issues discussed in the blog post
No, you'll just need to (potentially) keep the last 1-2 bytes of the previous chunk after each iteration. Come on, restartable UTF-8 APIs has been around for more than 30 years.
But those code points were just inputs to another stream transformation that turns a stream of code points into a stream of graphemes. Rapidly your advice turns into "just do everything in one giant transformation" and that loses the benefits of streams, which are meant to be highly composable to create efficient, multi-step transformation pipelines.
