This feels quite a bit like Fluid or Prism, as others noted. Interestingly, though, it looks quite a bit like writing a plugin for Chrome rather than a webpage (http://developer.chrome.com/trunk/apps/about_apps.html) and the new APIs are going to be interesting.
Integrating it into the OS might lead to unpredictable factors like Microsoft or Apple removing that kind of functionality from their future OS versions.
HTML5 apps were Steves original vision. Add to homescreen exist because that was supposed to be the way to deliver new apps to users on smart phones.
Why should Apple destroy that? To protect their 30% cut from a store that doesn't bring in a profit? For heavens sake why?
Apple makes money when you buy an Apple product. They want to make it so that you want to buy more Apple products, not fewer. If removing the capability to add HTML5 apps to the home screen causes a loss of just one Apple product sale, it is not going to happen.
Still, I like the approach Ubuntu is taking much more as it integrates into the desktop and is cleaner. http://techcrunch.com/2012/07/19/ubuntu-web-apps-aim-to-brid...