I personally do not want a smartphone with a 3D printed case and heatsink controlling my car. Do you hear that? It's the sound of a critical flaw in your product, no matter what you do technically you are never going to have a mass appeal product that becomes more than the nerds who hang out in your Slack channel.
But it's fine for a lifestyle business I suppose. You can market to them and sell them over-priced odb2 fit-bit-for-your-car dongles. Until Honda or whoever comes out with a "good enough" consumer grade "auto-pilot" (whatever that means these days because you still have to watch the car like a teenage driver), you'll loose a huge swatch of users right there who are only spending time on it to be on the cutting edge of tech and to look cool for their friends. Once it becomes a blender, those users will leave and go on to the next thing that grabs their attention in a banner ad. Or else people will get bored, loose interest after the first few joy rides with their friends. I'd imagine retention would be difficult in a business like that which takes a lot of sustained effort and engagement from the users.
The only possible path forward in this market is to partner with an OEM (car manufacture vroom vroom), have access to users, or make some kind of must-have tech that you can then con one of the real big money backed self-driving companies into buying. I've seen a bunch of web apps popping up lately that offer to annotate your training data, those seem like a lot better pump and dump tech companies than this dashcam that plays Pandora and runs some cool python PID controller.