Not a question, but we use 418 in production! We have a nginx router that routes pages based on its path to either old frontend or new frontend. I wanted some easy way to handle the routing (and to not repeat myself), so I set the new frontend as a handler for 418 error and then just return 418 in the nginx for any page I want on new UI. I chose 418 because the others could be actually used by the old frontend and it could get all weird.