Kuo released a forecast report in February 2019 claiming the entire next generation of iPhone will offer reverse wireless charging - something all the Samsung Galaxy S10 devices and Huawei's Mate 20 Pro support.
According to Kuo's report, the next iPhones will have integrated device technology that will allow them to charge the next generation of Apple Watch, suggesting the Series 5 could also see a change to the current charging functionality. At present, the Apple Watch requires a special charging disc, but this would need to be ditched for the next Apple Watch if the next iPhones will be capable of charging it simply by placing the two devices back-to-back.
Reverse wireless charging means you'd be able to place any Qi wireless charging compatible device on the rear of the next iPhone and it would charge it, like the second generation of Apple AirPods in their wireless charging case, for example, or the Samsung Galaxy S10 or the Huawei Mate 20 Pro.
Kuo also suggests that the while the next generation of iPhones will not switch to USB Type-C, like the latest iPad Pros, its charging cable will change to Lightning to USB Type-C. It's also claimed users will be able to switch the attached power adapter to 18W USB power, allowing for faster charging.
No further evidence supports reverse wireless charging on the next iPhones, but it is a feature that would make sense, given Samsung and Huawei are offering it on their devices. We'll have to wait a few more months before the next iPhones are announced to find out for sure though.