Great point, I realized soon after I posted and so I updated my OP. But still they could have gone with Android based system instead of QNX - it's open source, the Lollipop UI is gorgeous and since it would be a fork, there's no lock-in worry. Developers would be able to write / port apps and extensions easily as well.
It's a car. It's not going to have an app store. You don't want an app store. You don't need an app store.
QNX is a well-understood RTOS--look up "hard real time".
There's a lot more important things in a car for an OS than being able to display a notification on Facebook; things like deploying airbags, coordinating brakes, and all these other things.
Furthermore the notion that you'd be sharing core processing between safety-critical car functionality with infotainment functionality is downright scary. These should always be (are they?) discrete systems.
I can cause my BMW's i-drive (CIC-HIGH NBT F20 2013) to completely crash if I perform a specific action. After fifteen seconds the system detects the freeze and reboots. The way the reboot occurs strongly suggests the reboot is performed by a hardware level supervisor. But the rest of the car continues to function.
CarPlay and Android Car don't help you very much: They require a phone to operate. If you don't have one you get nothing. That doesn't sound like a big issue now but keep in mind that car multimedia is in development for about 4 years and then the cars are in the market >= 15years. This means if you now start to design a system around CarPlay you would need a iphone that supports the current CarPlay protocol in 2034. That's very unlikely. And when you don't have one you get nothing at all, neither music nor navigation.
Directly building a system on top of android instead of QNX or a custom linux distribution is certainly possible. Every approach here has some pros and cons. Keep in mind that not all of android is open source and available for everyone.
You can't directly use a normal Android phone UI because it is not certified for in-car use (driver distraction regulations). But you could at least use it's UI framework and some of the widgets. For the widgets there is the question if you want them. If they started development 3-4 years ago and based on android you would now get a brand new Ford with a Android 2.3 UI. Wouldn't look sexy either and even less in some years from now. Therefore going with some custom UI can make sense.
