My general aim with this is actually to just use the Dongle with a cheap Amazon Tablet, mount that in the car with some 3D printed parts and call it a day. Nonetheless it would be interesting to figure out the inner workings of CarPlay and maybe even get hands on the protocol either it or the China dongles use. This knowledge could be used to make "native" CarPlay on Raspbian or any other Linux machine that could do H264 decoding possible which would be pretty damn cool in terms of hackability.
But right now it looks kinda grim as the Firmware without the required (after some research seemingly non-public) libraries is somewhat useless and the Dongle App has been obfuscated pretty thoroughly which leaves USB sniffing or similar methods open. Honestly I don't think CarPlay without additional hardware is going to be possible in the near future because of the certificate requirements which you only get from Apple or by "stealing" it from Firmware images. This makes the intermediate black-box dongle that does all this and apparently has a certificate a way more attractive target.
EDIT: I can say one thing for sure though, almost all of the Apps out there for those dongles are from one source with minor modifications. Seems like either a white label solution or a *lot* of different versions out in the wild. ZBox seems to be slightly different though, still investigating.