This can work, but it's a fundamentally quite different async model and you give up a lot of the benefits because you have stackful coroutines, which are a lot

This can work, but it's a fundamentally quite different async model and you give up a lot of the benefits because you have stackful coroutines, which are a lot more heavyweight than the state machines which rust's async functions compile down to. There's nothing stopping you implementing this concept in rust today (a la gevent in python), it's just a seperate thing (and you still need to be careful about accidentlly calling something which does block).