"Would it also work for mostly-native games, or is it designed for Java-only?"
Technically, we replace smali which is working in java layer, but google's services are based on java even you invoke them in native, so it works for any game which can run on android .
In our elder product PrismSDK, we used this technology in over 300+ games covered in different game engine (Cocos2dx, Unity3D, native, java, even Adobe Air)
"I'm assuming you have some kind of middle layer that emulates google play In App Purchase on each of these distributers? Or would it be limited to premium games?"
It depends. If you insist on premium, we can only distribute it on 2 channels, it is limited but works. if you can make a change your game into free part and premium part, then it becomes a f2p game.
I love premium game, it always be high quality, I think it will be widely available in China's Android in the future, but currently, only 2 APK distribution channels supported.
Why exactly do your service need access to our Google Play account? (Slide 13, point 3)
Actually it is not needed it is optional. It is designed for get configuration for in-app product and store listing, we provide 3 way to do it, oauth login googleplay, export/import googleplay configuration, manually. You can choose one of them to do the configuration.
