no te desmiento que sea readonly, pero si es obsoleto.
Cita: location [Deprecated]
A Location object that contains the complete URL of the current document; a synonym for the Window.location property. In JavaScript 1.0, this property was instead a read-only string object that served the same purpose as the Document.URL property.
obtenido tal cual de "JavaScript
: The Definitive Guide 4th edition from David Flanagan".