[wtallis]

HDMI is first and foremost (and at times, almost exclusively) designed to serve the needs of TVs and related devices. Its presence on PCs and other devices outside the home theater space is largely a consequence of the fact that HDMI until recently was just a new connector carrying DVI signals plus some extensions.

The more relevant connector here would be USB-C, which can readily carry a mix of DisplayPort video signals, USB (including HID), and power, over a connector that is now universal for smartphones. A phone today connected over USB-C could handle all the processing for a very "dumb" car head unit. Aftermarket head units are mostly Android devices already, albeit not literally using USB-C internally.

[numpad0]

USB-C can't readily carry everything. There are specific and expensive electronic switch things on host side that has to be handled with gloves by experienced mixed signal experts. It's standardized and allowed, but you're on your own in terms of making it work.

Getting HID through HDMI is nothing compared to that. Just Arduino level stuff. It only has to be standardized for interoperability. Car brands that seek to disinfect cars of Apple/Google disease will benefit a lot from that.