iOS and smart phones in general has reached a ceiling. You can add better hardwares and new softwares, but the experience will be the same. The only notable improvement I can think of is to offer access to full fledge OS like OSX to run high quality softwares.
I wouldn't say that about iOS exactly, as there's always room for improvement on that front, but smartphones in general have.
We're all still riding high from the days when the mobile scene was still brand new, and awesome things seemed to come out every other day. While I think tablets still have plenty of space to grow, smartphones have matured to the point where we can't expect every new release to melt our faces off with brand new, unprecedented features that completely change everything we know about small computers that fit in our pockets.
It's moved into that gentle groove where everything is more iterative, like the PC scene during the 00's. We'll still see new things, but they'll be smaller, more focused and spaced farther apart. Now it's all about faster, thinner, better cameras, more battery life. Improving the concept, in other words.