My wishlist for the next iPhone would be:
ONE UNIFIED SIZE
I don't want Apple to release a 4.7 inch phone, a 5.5 inch phone, an iPad Air, an iPad Mini, the iPhone 5s, etc. I think Apple does it best when they keep it simple. The phablet market is overrated. 4.7 is fine.
MORE STORAGE
More storage meaning 32 GB = low end. 16 GB is fine for me, but it won't be. These apps are getting bigger, and high speed videos and high quality pictures take up a lot of space. 32/64/128 is fine, or just release an iPhone with an SD card slot.
THINNESS ISN'T THE MOST IMPORTANT THING
The one thing that bothered me about Jobs' design sensibilities is that he adored thinness over all physical attributes. It's nice, but there's no reason for a phone to be any thinner than the iPhone 5. Make it sleek, obviously, but most people would rather have a bigger battery than a slimmer device. Just ask any Moto X owner if they're upset at how thick the phone is.
FILE SYSTEM ACCESS
This is something that Apple won't do, but it's one thing from Android I miss. It's not that big of a deal though, and jail breaking isn't really my thing (I always root my Android phones, but that's because Android phones usually aren't good enough stock. Moto X and Nexus 5 change that.)
WIDGETS
I mean, it's about time, isn't it? Apple could even implement it like they do in OSX -- live webclips. A 4.7 inch display isn't very fun when it's filled with icons.
BETTER BATTERY LIFE
Not that I think there's much of a problem with the battery life in an iPhone -- much to the contrary -- (
https://forums.macrumors.com/threads/1707536/) but it can always be better. Fit a 2400 mah battery into the iPhone 6 and I'll be happy
PLASTIC ISN'T THAT BAD
Don't be afraid to design a more durable iPhone in plastic -- the 5c is actually the best iPhone to hold, while remaining sleek and beautiful with its unibody design -- there's nothing wrong with that. The 5s is more beautiful, imo, with its chamfered edges and magnificently machined steel while being ridiculously thin -- but that doesn't make the phone work better.
MAINTAIN THE RELIABILITY OF iOS
The thing that sold me back on iPhone was how reliable iOS was. It rarely fails me -- performing basically every task the same way every time. Android still falls behind here, greatly, with inconsistent design qualities and lag, no matter what phone you have. Don't tell me your Note 3 hasn't lagged, because even with 3 GB of ram, it has. Every Android phone does. Core system animations being built into iOS is a pretty big deal here. See how Apple has a flagship with a dual core and 1 GB of ram in 2014? Optimization. Try using the Note 3 with 1 GB of ram..there's no chance. Apple got me back because of their unwavering desire for a unified, beautiful experience. They don't bloat their phones with useless apps and features like other manufacturers do. When you use an iPhone you know what you're going to get -- and that's a lot of why people love OS X so much. As long as Apple keeps providing a beautiful, reliable, and CONSISTENT experience on their mobile devices, they'll have a place in this market. Stick to what makes you great, Apple.