Yes a lot of times the issue is that libraries only support certain version of React Native, so for certain sets of libraries there are no versions of React Native compatible with all of them.
The idea is that we provide a lot of nice things out of the box and then if you still need to write native code you can detach (https://docs.expo.io/versions/latest/guides/exponentkit.html) and only write the native code you need while keeping all our other APIs. You can still use `react-native link` after detaching if you want.
Is there a chance that some day your work (expo) will be merged with react native ? Conceptually, I think you are doing what people would expect the rn team to be doing. Namely providing access to the native apis through javascript, except that expo seems to provide much more features.
For me, what's holding me back from using expo is the additional complexity of yet another dependency and having to use more tooling (e.g. expo client).
I think right now it makes sense for us to be separate from React Native. Adding all of these libraries adds QA overhead and if Facebook doesn't use them internally it'd be hard for them to keep them up to date. In addition there are some other features we support that definitely don't make sense in core. For example we embed multiple versions of the React Native runtime in our app so that people can choose when they upgrade and we don't break old projects when we push a new version.