I don’t think users really know what will be the next thing that is super important to them.
Mostly people are looking for and/or expecting the usual: faster processor, brighter display, smaller bezels, better camera, and better battery life.
I would love to see a flicker-free screen, but most people wouldn’t care about that at all.
I suspect most changes will be software related. Perhaps iOS will allow split-screen multitasking, or improve widgets functionality and lock-screen aspects. There are rumors of an always-on-display which might be cool, but personally I’d just like my phone to still light up with a notification when I’m wearing my Apple Watch.