Actually, if you take this approach but with a twist, it's quite possible: As was shown with Google+ widgets for performance optimization, I.G.'s talks on High

Actually, if you take this approach but with a twist, it's quite possible: As was shown with Google+ widgets for performance optimization, I.G.'s talks on High Performance Websites and chatter from Polymer-using folks, deliver your first page, your template, using HTML. Pre-render things, but then make it interactive on-focus (if widget), or load your JS and continue loading data (mobile) or take your HTML and use it as starting point for a really nice template and loading framework for widgets (Polymer). The point then is that JSON is rather useless. It's not optimized binary for machine consumption, neither is it display-optimized DOM, in which styles and content can mix and interact. Oh and failure states are entirely possible to show. If you want a dumb failure state, code that for use when you introduce the loading spinner as a timeout helper. For more advanced failures, write the logic client-side as you would normally, then deliver and modify the HTML again as you would normally. No one says that because your primary communication mechanism for server updates is HTML that you can't in turn use JS on the HTML to provide updates between updates, as it were.