Well, apple makes the hardware, so they would typically make the drivers as well. From what I read and understood is that without being able to load own extensi

Well, apple makes the hardware, so they would typically make the drivers as well. From what I read and understood is that without being able to load own extensions you can only do whatever Apple allowed you to do. It could be compared to changes that Chrome plans (or already introduced?) to restrict extensions that filter sites which affect adblockers and you're at mercy of Google what you can block and what you cannot. Similarly here, you will only be able to hook to interfaces Apple provided, but if you plan to do something that wasn't thought of, or Apple does not approve, tough luck.