Yes, it's a set of libraries under one package name. With Google's massive investment in refactoring it has a pretty big surface already, from persistence to UI and almost everything in between.

https://developer.android.com/reference/androidx/packages

It's current implementation uses classes that are part of the Android layer, mostly the old support library plus some new abstractions like LiveData and Room and Navigation. I see no reason why you could not use the public interface of that library as a compatibility layer for application level code and let it run on a different platform.

Not today, but given the fact that you can't just kill the worlds most used operating system, you either use virtualization like Apple now does again for ARM (and before when replacing Motorola with Intel) or you change the underlying dependencies of the libraries used and compile again.