> If anything, top level async would be an improvement, as it would give developers no reason to do synchronous IO.
Top-level async would make asynchronous IO no different from synchronous IO! It's the worst of both worlds.
> the dependencies are statically analyzable
Exactly – which means modules can be loaded concurrently, without having to execute the code. By contrast, imperative loading has to happen sequentially. I explored this aspect of it in a follow-up: https://gist.github.com/Rich-Harris/41e8ccc755ea232a5e7b88de...