I think libraries like Lwt will be the ones to offer the level of abstraction which you're describing. I too would like to see the simplicity of goroutines make it into OCaml 5 ASAP.
On parentheses, this is one of the main reasons why I integrated ocamlformat with my editor: I write explicit parentheses around everything and I let the formatter remove the superfluous ones. No surprises or guesswork that way.