All iOS CarPay apps have to be approved by Apple in more then the normal Appstore way, which is why there is limited apps that work, I imagine its to prevent people becoming distracted with apps while driving...
The other issue is that the App will have to connect to the Car to read all of them commands, Apple is working on allowing 'CarPlay' to talk to the car (to control heaters, drive modes, etc etc) in the future... I doubt we will ever see it in this VAG MiB2 version of the system though... VAG have also said this version MiB2 will not support the 'wireless carplay' feature. It is believed VAG have some hardware for wireless for demo, however Apple have not allowed them to demo it - Apple will probably announce something at the next iOS Dev event (WWDC - around June). Probably see hardware upgrades in the '2017' facelift versions of the A3/Leon/Golf etc.
Isn't it great how technology never stands still?