Many cars can be modified even now with increasingly integrated entertainment systems. Beatsonic or its various Chinese copies are an example of this, it’s a box that hijacks the video stream and lets you add CarPlay functionality and stuff.

Car manufacturers have money. They can and will lobby the monopoly status quo.

Money talks. I know it's hard when you want that nice car, but considering the above, the only way is just not buying the car with software lock-in. Only this stimulus can have some effect.

There is. You can swap out the head unit with an aftermarket one.