On some thread I read here, someone mentioned Microsoft doing programming languages researching this. I didn't find that post when I last mentioned the existence of said post.
I tried looking for the paper. So far, I found a different paper on implementing the original ideas in C. I'm only kind-of sure this paper is connected to the one I sort-of remember, but it does talk about async & await. More web-searching (on "microsoft language with first class effects") has found another paper, which lead to a preceding paper, which may have been the one I'm trying to remember. Maybe check the three (other) threads here that reference "koka."