You have that backwards. Tesla uses the open standards available on all phones to facilitate communications between the car and phone. So Tesla has all the code for sending and receiving audio over bluetooth and they don't care what device is actually connected on the other side. They also use the open standards for sending and receiving text messages - again, it doesn't matter whether your phone is Apple, Android, Backberry, Microsoft, etc, whatever - if it complies with the standards, it works.
If Tesla is going to make CarPlay work, then Apple should publish an open standard that everyone can use.
But honestly, go to a Tesla store, pair one of the display cars with your phone, and tell me that CarPlay offers anything that the car doesn't already do better. You can already call or text anyone from the car. It'll both read and display text messages on the screen, vs CarPlay which only reads them. The car has Spotify, Podcasts, and plenty of other audio apps built in. It also has Netflix, Hulu, YouTube, and other video streaming apps. Plus a web browser able to use video conferencing programs.
Honestly, asking to use CarPlay in a Tesla is kind of like asking to use CarPlay on a Mac. Why? The Mac already has native apps to do everything that the iPhone can do, and then some.