1. export_libraries could be optional (actually the whole module.json could be optional).
2. abi.json could contain an optional 'link' to the binary (relative to the AAR root). This way, a conventional AAR could be reused for prefab by adding a fixed prefab tree. That would be as easy as building a prefab tree structure under src/main/resources of a library module.

Well, include files may require special effort to be in sync with the source tree, but there are some tricks that make this easy on Android Studio.