I don't really think the ownership-related concerns around thread-local storage that ruled out stackful coroutines are valid. Stacks and threads are orthogonal

I don't really think the ownership-related concerns around thread-local storage that ruled out stackful coroutines are valid. Stacks and threads are orthogonal in the same way that futures and threads are orthogonal in the existing design for async. This design has caused a proliferation of dozens of fundamentally non-composable libraries addressing barely-different use cases and leaving many use cases unaddressed, likely wasting much more time than it would have taken to get this right. Various prior art has existed for decades. I accept that languages that are designed collaboratively by huge numbers of people through an RFC process are basically impossible to improve.