> use async/await syntax for arbitrary monads. (In JS, it is even easier to bend async/await to arbitrary monads given the rules of a "thenable" are real simple.)

I tried once to hack list comprehensions into JS by abusing async/await. You can monkey patch `then` onto Array and define it as flatMap and IIRC you can indeed await arrays that way, but the outer async function always returns a regular Promise. You can't force it to return an instance of the patched Array type.