I think Apple since the launch of the iPhone 6 have been aiming to append users existing mental model and offer alternative ways of navigation other than the UINavigationBar. As the article mentions, left swipe and reachability features are clear admission that Apple are offering users additional ways to navigate back other than the hardest to reach area.
I agree that context is an issue if the UINavigationBar is removed completely, however it can still persist when relocated. Dare I mention it that Metro UI positioned this at the foot of the screen and although I little odd at first it was a UI that once familiar was simple to use.
What’s also interesting is that the current UI was developed before any iPad or iPhone larger than 4inch. So what ever Apple do decide will impact on those products that users don’t just operate with one hand. How would a relocated UINavigationBar work on an iPad used by both hands?