It seems another bold move by Facebook, considering that it dropped HTML5 a few years ago because they could not get the UX to work uniformly on both iOS and Android. This led to the complicated task of writing separate apps for iOS and Android, which invariably led to the React library.
Since JS is a development language that pretty much all web developers know, React-Native has the capability to become a mainstay with developers who can quickly transfer/code apps between platforms, which would most likely lead to React becoming a self-sustaining open source project. JS is already open sourced and already has many libraries that can be combined with React to further accelerate development.
While the developer will still need to write different user interfaces for the different platforms, the core build of the app will be the same which can significantly cut down on development time – hopefully eventually leading to the ability for developers to write the app once and have it run on any platform.