Well here's a list of directions, with the caveat that you'd actually have to try some of these to see what worked. Improving safari with smart 'readability'-esque relayout engine. Safari performance for webkit. Widgets. Lock screen apps. Built in speech-to-text api. Flutter like non-touching gestures and interaction. Augmented reality api - with maps data. A todo app and api/data store (ok you'd make a million app developers cry with that one). iCloud for data.
Of course some of these are available as third-party apps and apis. Some would suck (widgets for one probably). But I don't believe we're anywhere near running out of things to innovate on to make mobile computing worthwhile/suck-less.
I was thinking on phone processing of speech, not sure how much difference it would make. The point of that list isn't that those things don't exist, but they are areas where Apple could push hardware, operating system and web services in order to do something innovative in mobile computing.
Of course some of these are available as third-party apps and apis. Some would suck (widgets for one probably). But I don't believe we're anywhere near running out of things to innovate on to make mobile computing worthwhile/suck-less.