You just described exactly what you're _supposed_ to do in a progressively-enhanced single-page Javascript application. Build the existing site first without a

You just described exactly what you're _supposed_ to do in a progressively-enhanced single-page Javascript application. Build the existing site first without a single line of js, develop the hash-bang/HTML5 history syntax on top of it, and replace the links if javascript exists. The Gawker family of sites failed at doing all of this.