std::future was caught in coroutine/network/concurrency/parallelism master plan that has been redesigned way too many times. Sender/Receivers is the the current direction, and while I don't dislike it, we are still far for a final design to cover all use cases (we still don't have a sender/receiver network library proposal I think).

Whatever we end up with, std::future just wasn't a good base for an high performance async story. Still just adding a readiness callback to std::future would make it infinitely more useful even if suboptimal. At least it would be usable where performance is not a concern.