Customers get access to a private repo for latest updates and priority support for 1 year (yearly maintenance fee = $150/year). ~20% of customers pay the yearly.
Each purchased key is bound to a mobile app id. If customer wants to make 3 apps, they need to purchase 3 keys.
Public repo contains latest stable release; purchased keys unlock product in public repo forever.
iOS lib is free. Only Android lib requires a key to unlock it. This gives users the chance to freely develop iOS first (and hopefully get hooked, like cheap crack ;). Chances are they're going to release an Android version too since most of the earth uses Android.
The Android version is fully operational in DEBUG builds. Key is enforced for RELEASE builds.