Whilst your approach kind of works, I feel this approach is a lot better because it doesn't litter $async around your codebase, and also will work with async ES6 class methods.
If you feel the same, it might be worth updating the readme and republishing the module so that other people googling how to do this also know about doing it that way, as opposed to also having to put $async around their codebase.
I would recommend doing it this way: http://debuggerdotbreak.judahgabriel.com/2017/04/24/making-typescript-asyncawait-play-nice-with-angularjs-1-x/
Whilst your approach kind of works, I feel this approach is a lot better because it doesn't litter $async around your codebase, and also will work with async ES6 class methods.
If you feel the same, it might be worth updating the readme and republishing the module so that other people googling how to do this also know about doing it that way, as opposed to also having to put $async around their codebase.