Bring back the headphone jack. Matter of fact, just put multiple headphone jacks all over the phone. But by then, people will have moved onto Bluetooth and won't even want headphone jacks. Even the most diehard of 3.5mm fans.
So what one function? Does long range wireless charging count? If apple could implement this and make it usable, it would change so much it's ridiculous. Thinner phones + having your phone charge the second you walk in the door at home. The second you walk into a restaurant or mall. Never even thinking about a battery percentage. And then watching this technology propagate to other things like ipad, Apple Watch and MacBooks.