He said, and I quote:
With this, it will be possible for them to create themes that are built using other languages, which has the potential to improve website performance and also to create new and more innovative websites.
The REST API is huge. People haven’t even begun to scratch the surface for what this feature will mean for the future of WordPress – after all, it was only added to the core a month ago. This new way of working with WordPress can change how it is used forever.
So far there have been new themes designs, and some mobile apps. There’s so much more potential still to be unleashed. There’s the IOT to think about, looking at how the API can be used to control smart fridges and the like. Smartphone apps, new admin interfaces, inventory control management, there’s just so much scope.
Anyone who wants to be at the forefront of WordPress development will need to learn new skill sets to stay ahead of the game.