A bit of a tangent: it might be a really particular use-case, but I kind of wish that Chrome's <webview> (http://developer.chrome.com/trunk/apps/app_external.html#web...) was a universal HTML5 feature for secure rendering contexts (extensions; file:// URLs; node-webkit, AppJS, and other HTML5 "platforms"; etc.)

It would be great if, in those use-cases (where clickjacking isn't a problem), there was a guaranteed way to have a page load in an iframe-like context, but with a separate renderer, separate JS state, asset(window.top == window.self) passing, X-Frame-Options passing, etc.