The coordination needed to do that is tremendous, especially when you get into versioning. A dedicated companion app is better. "Hey user, if you want to use this feature XYZ in my app, install this other app so mine can register with it". Makes the UX dead simple for both users and developers by moving the overhead to a single application & thin IPC client library for other apps to import and configure (just like registering with Play Services Framework).

It shouldn't be that hard to do since I already implement it as a Service. Bad news is that I have no idea how to define it as a lib, I need to dig into it.

...but any help is always welcome!

You might need to do a Content Provider for your DB. Otherwise each service will have their own DB. Ideally if Primal and Amethyst both import Pokey, we can start a single Pokey service while sharing the same user settings. Starting from Amethyst or from Primal should yield the same service.