It doesn't mention him by name, but he's the "language designer of some renown" alluded to here:
If you were a language designer of some renown, you might convince a large and wealthy technology company to fund your work on a new language which isn’t so beholden to C runtime...
Ah, thanks, makes sense. I largely skimmed the conclusion, so I guess I didn't make that connection.
I did think about Go throughout the article, since it basically uses "green" functions everywhere. I guess I got tripped up when they mentioned "effect handlers," which isn't a thing in Go AFAIK (then again, I'm not a language designer), unless it's used under the hood.
In a less than optimal world, you might decide to do something less inspired. You might take that break from the C runtime and then just implement threads again, with basically the same semantics, except that they are scheduled in userspace. Your users would be required to implement concurrency in terms of threads, locks and channels, just like they had always been in the past. You might also decide your language should have other classic features like null pointers, default constructors, data races and GOTO, for reasons known only to you. Maybe you would also drag your feet for years on adding generics, despite frequent user requests. You might go do that, in a less than optimal world.
just implement threads again, with basically the same semantics, except that they are scheduled in userspace
To be fair, the Go implementation here is quite interesting since it scales way better than OS threads, so there are fewer downsides to spinning up a ton of threads. So it's closer to async abstracted behind a threading veneer, like the GREEN functions in the article.
Though the "known only to you" criticisms are absolutely on-point.