Suppose you were to make an f-droid like client without a source code requirement. A way for people to host their own proprietary applications, and a client app

Suppose you were to make an f-droid like client without a source code requirement. A way for people to host their own proprietary applications, and a client app that can manage repositories the way f-droid does. How would you: - make applications/repositories discoverable without running a service, - allow developers to handle billing for paid apps themselves, again, no service, - have client side malware protection without playing a cat and mouse game, - prevent discoverability of pirate repositories without running a service? If these problems can be solved (or others I didn't think of, maybe you did?) you can basically get rid of monopoly curation of available applications on android (or anywhere for that matter).