Is this a bug report?

No.

I am interested in extending a Component, provided by react-native with some native code. The closes example I can find is react-native-maps. It feels like they are extending the MapView component (since the Components from airbnb and facebook have the same name) – but I am only guessing here.

So, lets say I would want to extend the component with these peaces of code (android, iOS.h/iOS.m) and expose something like this on the frontside in react-native:

<MapView.UrlTile
    urlTemplate={someURL}
    />
</MapView>

How would I go on about it? For every hint I am grateful.