iPhone users who buy new models with USB-C would have to replace any old stuff that uses the lightning connector. All this proposal would do is force a bunch of stuff to become obsolete.

How would it significantly reduce ewaste? Most phones - including the iPhone - come with a cable that connects to a USB-A or USB-C port. I guess it would reduce the amount of male lightning to female USB-C dongles manufactured, but that seems pretty inconsequential.