In reply to Daan van den Bergh.

The Web Fonts API is actually the equivalent of the existing Scripts and Styles APIs. It adds a wp_register_webfont() and related functions to go along with the wp_register_*() and related functions for scripts/stylesheets.

If you're asking if there is an equivalent theme.json implementation for scripts and stylesheets, that does not exist. Well, technically, theme.json allows a standard set of CSS configurations, but that's it. I haven't seen any tickets that explain the use cases, but I can think of a few scenarios where it might be useful.