They are already in Clojure. You can easily do (future (some-async-work)) or promise and deref that later or use any other kind of JVM concurrency util like ExecutorService. The issue that you can easily do a blocking deref without your whole program deadlocking but JS needs native syntax to emulate this. It still isn’t anywhere to close to actually being able to block but the code does look much more “friendly” overall.
Besides that generators are just a more generic version of the IOC code rewriting the core.async go macro does. In fact you could make cljs.core.async significantly simpler by using generators. js-csp works like core.async but completely without macros. This would make core.async a lot easier to debug and it would generate way less code as well. Closure also has no issue with translating the code to ES3 if needed.