I posted just 2 months ago about Foxhound and how I found it pretty cool, but also curious that it was one of very few themes around that combine the WordPress JSON API and React, even though they seem like a perfect natural fit. Like a headless CMS, almost.
Since then, a few more things have crossed my desk of people doing more with this idea and combination.
Maxime Laboissonniere wrote Strapping React.js on a WordPress Backend: WP REST …
WordPress + React is a post from CSS-Tricks