Surely server-side: Node > 6 supports ES6 without transpilers. Since Node doesn't have to be browser-compatible, there is no reason to use older versions.

On the client side, I recently wrote a CMS for a big company based on CSS flexboxes (which are not polyfillable). I also wrote a number of browser projects using ES6 / ES7 features, but normally you demand transpiling and polyfilling to Babel, so you never know.