The react-native-implementation.js file still uses Haste as a way for Facebook to internally run different RN JS than the code on GitHub. This issue is primarily about finding a way for Facebook to maintain a separate implementation of modules from open source while migrating at least the open-source implementation of react-native-implementation to use path-based imports.

This is probably best to work on inside of Facebook since it will require changes to the internal repo and maybe the build system as well. Ex: one idea is to give Facebook-internal modules .fb.js extensions that Facebook's bundler configuration prioritizes over .js.