What I want from the iphone 6 is first an foremost notification leds. While not essential, it would be very, very nice indeed. I also want better word prediction with swype functionality built in - not a separate app download. It must be on par or better with swiftkey on Android.
Obviously a bigger screen, which is not just something that would be nice to have, but an absolute must. I wont even look at iPhone 6 if they will not enlarge it.
Also, don't know if it's just me, but in-call quality has deteriorated from 4s to 5 and 5s. It's just not loud enough! Seriously, I have good hearing, but the phone is not loud enough in calls!
I also want a better, speaker as in HTC One. (Not gonna happen, but I can dream...)
Finally, further improvement to camera would be nice. Oh, and expandable storage? (not gonna happen, I know.)