And at the other end of the MacBook, it seems the USB-C hardware has also changed. The cable is now perma-fixed to the USB board, condensing the two components into a single unit.

...Also, the silicon is new and moved from the cable itself to the USB board. Here's a comparison of the new USB-C hardware (top) with that of the 2015 Retina MacBook (bottom).

Parade Technologies PS8741A (likely an iteration of the PS8740 USB-C redriving switch)

Diodes Incorporated PI1EQX7502 USB 3.0 redriver (likely)

NXP Semiconductor CBTL04043A1 4-Ch. bidirectional crossbar switch

This new USB and cable arrangement is one thing that's not compatible with previous Retina MacBooks.