Starting September 21st, a new merge proposal for a REST JSON API was opened on WordPress.org. At the moment, the REST API is developed as a separate plugin, but the implications of integrating it directly in the WordPress core could be huge.
The idea of using APIs to access WordPress data is not new in any case, but the way this has been done in the past was proven to be hugely ineffective. APIs are designed as a communication means between WordPress and another piece of software, like an application or 3rd party platform. They might not seem important, but, in reality, an API empowers developers to have direct access to the data (without going through a browser) and build new ways of displaying it, outside of a classic WordPress theme.