Why should we fix something not yet broken? While users of pug may be jaded, and users of coffeescript see its features becoming native in one framework after the next, the attraction to await/async is that it is almost universally embraced and expected to grow in usage due to its conciseness. One could argue that transpiling await/async can create a degree of code bloat, its terseness and existing or coming inclusion in all major browsers should moot that argument.
If you currently transpile your code, replacing promises is something you can begin today without breaking anything. That said, check out a new branch just to make sure!