Before we go on, this is a rumour from the supply chain which suggests this drastic change in port type should happen on the new iPhone, in 2019. So it likely won't appear in the iPhone 2018 line-up expected this September.
According to the inside source, Apple is redesigning its chargers and interface for the next-gen iPhone and iPad gadgets. With USB-C already found in Apple's MacBook, this device wide adoption makes sense.
This follows previous rumours that have suggested Apple will throw in an 18W fast charger with its new iPhones this year. This should save people money while also enabling the fast charging capabilities of the iPhone for a zero to fifty percent charge time of just half an hour.
The current MacBook and iPhones won't be able to run off the same charger, most probably, due to varying power input abilities. But perhaps in the future Apple will have one charger to rule them all. We can but hope.