It's ironic - the addition of extensions, custom keyboards and the like was possibly going to be enough to bring me back to iOS from Android - I always preferred the hardware, just wanted a little more flexibility from my software. But now Apple has totally ditched the 4" hardware factor - the main reason I liked the hardware so much. To me, Apple has lost an edge by doing that.
eh, totally ditched? the 5s and 5c remains available.
For example: The iPhone 4S was released in October 2011. In October 2013, Apple released iOS 7. While iOS 7 supports the 4S, it increases RAM overhead to the point that switching from app A to app B kills app A the vast majority of the time. (This is terribly annoying when you're writing, you switch to a web browser to look something up, and when you switch back the thing you were writing disappears.)
The user adoption rate of new OSes is ridiculously high. This means you will have maybe 3-6 months after the new OS comes out before apps no longer support the old one.