There are plenty of aftermarket head units for specific cars.
It's not that hard for the manufacturers to make another plastic part.
You shouldn't have to though, now that there is this dual communication standard.
If your car has space for a head unit, and a fascia is available, and a steering wheel controls adapter is available, and a backup camera adapter (sometimes eight needed for the cars with "birdseye" view systems), and a climate control adapter, and sometimes a navigation system adapter, you might be able to seamlessly install a headunit. It just might cost a lot.
For most modern cars, it's a pipe dream.