work has already begin on a direct-style IO library that internally uses effects. See:

- https://github.com/ocaml-multicore/eio#readme for more information on the Eio library - https://watch.ocaml.org/videos/watch/74ece0a8-380f-4e2a-bef5... is a short talk on experiences using effects with some nice motivating examples

Note that Eio is more than just a direct replacement for Lwt and Async. We couldn't resist using some of the experiences also gained from the MirageOS (mirage.io) unikernel framework in EIO. This means that the backends are highly optimised to use the best syscalls available in the OS (e.g. io_uring by default in Linux). If you write your applications to use Eio natively, then performance is very high so far. The ergonomics of programming in it also compare favourably to using monadic concurrency.