Last year there was a rumor that indicated that Apple had decided to change the connection Lightning-USB-C, however, at the end it was a bad interpretation of a document filtering, but now everything seems to indicate that Apple is determined to bet on the USB-C, because the Lightning is no longer a connection as advanced in comparison with the USB-C.
This has been mentioned by Digitimes, which indicates that the first iPhone in offer USB-C will arrive in 2019, which will also be the first generation where all of the devices are committed to an OLED screen.
It is said that Apple wanted to implement the change to USB-C from this generation, however, make adjustments in the production was costly and because it was not simple to implement, reason why I have decided to wait until next year.
Despite the fact that this is a strong rumor, it was a situation that would end up happening sooner or later, because we must not forget that Apple has already adopted a complete USB-C on their MacBook. In addition, a detail that we cannot ignore is that the European Commission announced that by 2020 would impose a standard, probably based on USB-C for manufacturers of smartphones use yes or yes, this connection.
This means that Apple would have to abandon the Lightning, at least in Europe, and I doubt that the company prefer to keep both of these connections instead of using USB-C for all your devices.