You don't have to use CarPlay, but cars will have full digital interfaces, so you can use CarPlay or the automaker's interface.I don't really want CarPlay to take over the whole car. I wish Apple would update their existing interfaces instead. Map apps seem to disallow any kind of interaction with them. I can't find a way for Apple Maps to display a list of upcoming directions. Messages are probably the most annoying since it forces you back into CarPlay just to display a dialog box that asks if you want to hear the message instead of just showing the message.
Podcasts don't want to show more than a dozen or so episodes. The Now Playing button is on the far right of the screen, far away from the driver.