The latest talk of USB-C replacing the venerable Lightning port comes from a new DigiTimes report that says that both the iPhone and the iPad will make the jump in 2019. The Lightning port has been with us ever since 2012 when the iPhone 5 was introduced.
Today, however, USB-C has become commonplace for new mobile devices. Thunderbolt 3/USB-C ports can be found on desktops, notebooks, convertibles and the vast majority of new Android smartphones. Even Apple's MacBook/MacBook Pro family has embraced USB-C, leaving Apple's iOS devices as the odd man out.
By adopting USB-C, Apple will be able to cut down on the number of adapters and cables that its customers will have to purchase. For example, an iPhone cannot sync or charge from a MacBook Pro with the cable that is included in the box. Customers have to purchase a $19 USB-C to Lightning cable to achieve this simple feat. And if you want to enable true Fast Charging support for your iPhone 8, iPhone 8 Plus or iPhone X, you have to purchase a $49 30W USB-C power adapter (which doesn't include the cost of the requisite USB-C to Lighting cable).
It's said that Apple is currently in the "redesign phase" of development for its 2018 family of iPhones, which means that the chances of the USB-C port being included this year are slim to none. So, the earliest that we'll see these alleged new USB-C equipped iPhones will be in the fall of 2019.