Tesla aren't as open as they seem to be. This is just the API between the phone app and the Tesla servers. As far as the car itself, they are pretty closed.
There was a thread a while back on a Tesla fan forum where people had figured out how to access the internal ethernet network between the two displays. One guy managed to SSH into the drivers console and bring up Firefox via Xorg. Tesla told him to stop or they would void the entire car warranty (they were monitoring his access !) They were getting access to loads of useful data, like the raw battery energy available in kWh, but they stopped because no one wants a $100k brick.