That would be awesome to see on a modern tablet device. The gesture interface already exists and people are accustomed to it. It would be neat to see a demo of it at least.

Thinking about it, while not implemented for the whole experience, are there any apps that do this?

To some extent Safari on OS X does this now (since what version, I'm not sure). While you can zoom in and around a page, you can also zoom out when the page is at 100% and get a view of all the open tabs. iPad with its multitasking control is similar (swipe up with 4 fingers to see all tasks, tap on one to switch to it). A photo app would, as demonstrated, be an appropriate use, same with the calendar. Instead of having to hit buttons to move up the hierarchy allow the users to pinch-to-zoom instead.