I still have reservations about the capabilities aspect of Eio, but the structured concurrency part looks very nice.
Just a few notes, for future reference to readers of this thread (if I haven’t missed them being posted above already):
Another interesting post about structured concurrency and cancellation: 250bpm
A structured concurrency library in python: trio, which might be relatively similar to Eio’s switches in concept (esp since @talex linked this)?
Companion post to the trio blogpost: Timeouts and cancellation for humans — njs blog which is directly relevant to the current topic.