The team is now working on the WordPress Interactivity API. This unblocks the same UX Frontity framework enabled but directly in WordPress Core, fully compatible with the new Site Editor.
Frontity uses a library called Emotion to handle styling, as you might know. Emotion creates the CSS class names and will automatically pass the classNames prop for you. But if you are styling some existing component, Emotion needs to “know” where to pass that className prop!