iOS 7 apps typically use a left to right edge swipe to go back to the previous screen, the SE app should do the same
Pages not utilizing edge swipe:
- Tags/Search page
- Site Index Page
I was able to help you a little bit. iOS by default disables swiping back when you set a different left bar button item or hide the navigation (which happens in the case of search). I've reenabled it when search is active.
When you go to a site's index page, you are actually taken to a new root view so navigating back won't be possible without redesigning the app. We could have swiping open the navigation but that is already possible at any point from the navigation bar.