React has, from day one, sought to liberate itself from the underlying low level building blocks of a particular environment. There were always good reasons to so (normalizing browser inconsistencies etc). There is another benefit of the specific way in which we've built this library level layer of abstraction - we've formed a serializable boundary that allows vanilla React to sit on one side, and any set of lower level building blocks on the other. Before today, we simply had the DOM renderers sitting on the other side of that boundary. React Native replaces the DOM renderers with native renderers which allows people to render platform <View>/<ScrollView>/<NativeWhatever> instead of <div>/<span>. Other than that, you get to use the exact same React API that you already know (even down to the event bubbling). You can bridge to things that are only available on the platform, and can in general make higher performance granular building blocks that cannot be accomplished with web technology (such as <Image> components that decode images more efficiently or with different concurrency models). As with everything, JSX is not required to take advantage of this - and you can use any of the compile-to-js languages that you use with React today.

iOS and android right now. And yes, native components can be rendered directly with JSX. And you won't need to mix with DOM. <h2> For example doesn't mean anything on iOS.