In 2012, when RFC 7238 was approved, we went for Experimental because it was, indeed, an experiment. Since then, it has been implemented in Firefox and Chrome, and Safari already supported it due to their default handling of 3xx + Location. The experiment is, therefore, over, and was a success. This action moves RFC 7238 to the Standards Track, as Proposed Standard. The document doesn't need any changes, and no updated RFC is required.