I am not sure their are a lot of use-cases for this where there is not already a great java or c++ library. So I fear that it might not make a lot of sense to u

I am not sure their are a lot of use-cases for this where there is not already a great java or c++ library. So I fear that it might not make a lot of sense to use Rust for most apps. Regarding the API, IMO a solution can only come from Google. There are good arguments in favor of replacing Java by Rust (or a Rust inspired language managed by Google) and even to rewrite the app framework foundations in order to improve the current offering. Officially, Java is the language of the platform, but that does not necessarily mean that they won't replace it in time.