My guess is that some non-insignificant (though certainly not large) new portion of buyers will replace their head units, assuming they keep the double DIN standard. It's trivial to change out currently.
Of course if too many people do it they'll change the slot and make the wiring harness an incomprehensible mess. One wire now controls your left rear audio channel, rolls down all your windows, and deploys caltrops if the police are behind you. If you wire things incorrectly it locks you in and sets the car on fire.
I'm using HoloISO (it's like 95% SteamOS) on a mini PC (all AMD, 680M iGPU because I wanted to get close to the deck specs). I mostly stream games from elsewhere in the house, but it has a few titles installed locally.
The sleep works perfectly so far for local titles. I assume other Arch based distros with all of the steam software installed (like ChimeraOS) work just as well. If the hardware maker who puts it on their box makes sure their hardware is well supported it shouldn't be an issue.