I think what we need is a mix between a module bundler and package manager. When you pull in a dependency, it should confirm the code can run on all your targets. If it wouldn't run, e.g. ES2015 classes but you have an ES5 target, it should be compiled. That way when you bundle your app, you can skip the compilation check on all third-party modules. Adopting an incremental compilation strategy will also speed up larger apps.