Nothing prevents anyone to use the USB-PD protocol over a different cable and plug (and maybe some do but we don't know it) rated for 10A. It's just so much more practical both for users and when designing to just use off the shelf USB-C (which AIUI has its design rated for 5A) as the physical part.
Thanks! That's exactly why I was looking into the comms side but didn't spend more than a couple moments on the cable side. I was considering building something that had board-to-board connected modules and used PD to negotiate the power between boards.
