The authentication will indeed be a tricky one to tackle. This project shows how another device has done the mfi authentication, which was then hijacked for communication over serial. https://github.com/ndusart/freedelity-lightning
Implementation of the mentioned protocols (which presumably are also documented for mfi developers) should be a breeze from this point on.
Now that software authentication is possible, i'm sure it is still no easy task, but at least became much more promising to spoof. Maybe a construction where the Pi forewards authentication traffic to an actual authentic mfi carplay device somewhere on the internet, and then again hijacks the line, much like the usb hardware variant.
Can anyone point us to more documentation on wireless mfi authentication?