Oh certainly, it's just beyond what I can do as a C library. I've also seen another approach that implemented a customized libc replacement to allow this to work. But that and modifying the compiler itself are really extreme steps.

It's still doable, and it's definitely worth doing, but I understand the uses I've mentioned are rather niche, so it's unlikely to occur. For one, we still don't have built-in stackful coroutine support even in C++20.