Earlier this week a report from The Wall Street Journal suggested that Apple could be getting ready to dump the Lightning connector in favor of USB-C. But it now appears that it's not the iPhone that could be making the switch, but the cable.
According to a research note written by KGI Securities analyst Ming-Chi Kuo and obtained by MacRumors, it comes down to fast charging:
"We believe all three new iPhones launching in 2H17 will support fast charging by the adoption of Type-C Power Delivery technology (while still retaining the Lightning port)."
So, the bit that could switch to USB-C is not the end that plugs into the iPhone, but rather the other end. This would mean that owners of Apple's new MacBook Pro (which is equipped with four USB-C ports and nothing else) would be able to charge their new iPhone directly.