Apple is expected to transition its iOS devices to USB-C connectivity later this year, by shipping a Lightning -> USB-C cable and a new 18W charger, previously rendered here. This will move new iPhone buyers over to using USB-C for charging with a cable. It will also mean that customers can take advantage of Type-C fast charging without needing to buy additional accessories.
Next year, Digitimes reports that Apple will add USB-C ports to the iPhone itself. This would be a major shift for the product line and would presumably be the beginning of the end for Apple’s proprietary Lightning connector.