Promises (which aren't limited to JS) are about far more than pretty syntax. Promises and promise combinators give you guarantees about your code, such as "no promise will ever execute both its success and failure callbacks" and "of the callback that is executed, it will never be executed more than once," and "once a promise is resolved, it's state cannot ever change."
Also, I don't understand the benefit of being able to learn a language in one day. You can learn how promises work in a single day and then apply that to any language that implements them. With Go, you will learn the language but then have to re-implement promises for every type that you have [0].
Consider the use case of issuing two API requests concurrently and assembling their results. You can do this using the fan-out, fan-in pattern described at http://blog.golang.org/pipelines
Search the page for "func merge". Any time you want to fan out and fan in, you will have to write that block of code for the types of the channels you have, or else use interface{} and lose type safety. So the cost of a language that can be learned in one day is that every single time you perform this very common concurrency pattern, you will have to repeat this code and potentially make errors in the process. And if you want to change how this merge pattern works across your codebase, you will have to change it in many places. What happened to DRY and reusability?
[0] There is a Go promises library, but it uses interface{} for all callbacks and does not appear to have been an active project over the past year. https://github.com/fanliao/go-promise