2 More Stable iOS
This isn’t strictly an iPhone feature, per se. But it is related. This year’s iPhone X launch has been marred by the instability and general bugginess of iOS 11 — ranging from battery drain to a software-side cold weather bug.
To be fair, pretty much any major software release will have bugs present, even with extensive beta testing. Though for a company as massive as Apple, there aren’t many excuses for extremely buggy software. It would be nice if Apple doubled-down on getting iOS 12 to be as stable as possible before the 2018 iPhone lineup drops.