To do user space concurrent software efficiently, one really needs at least some degree of OS cooperation. Only the system knows what kind of work is running on the machine and what the relative priorities are. One problem with the common executors is that they attempt to grab all the resources the system can offer - if you have multiple applications like that, you end up with extra thread contention. I also agree with the article in that the common coroutine as state machine model has its pitfalls.

With all this in mind, I really like Swift concurrency runtime. It does automatic thread migration and compaction to reduce the overhead of context switches, balances the thread allocation system-wide taking relative priorities into account, and it appears to be based on continuations instead of state machines. A very interesting design worth studying IMO.