The navigation on your phone is probably better than the one in your car right now, but when Apple or Google take over the car system market you will have Apple CarPlay or Android Auto in modern cars that have high quality software with fast update cycles. There is no reason why the same thing won't happen with TVs. In fact as mpeg, stated if you assume the firmware in your next Smart TV is open, it will be possible to run customer operating systems such as Android or XMBC giving you complete control without the external box or wires.
Edit: Though what you say about hardware refreshes is absolutely right.
The best compromise would be car-as-peripheral; have all the buttons map to a USB HID device connected to a flush-fit tablet dock. Just remember not to bridge the UI directly to the same CAN bus as the fly-by-wire throttle.
I have a 2300 pound, 2014 model year, gasoline powered bluetooth speaker, exactly as you suggest. In the showroom they had a "smart nav smart entertainment system" upgrade for only $1200 that was as much of a turd as the typical smart TV. Its hard to buy a dumb-stereo for a car that doesn't have BT pairing today.
Mostly I stream podcasts and audiobooks from my phone. Hit play on the phone, put the transmission in drive, thats my commute.
Yes, it does. When it comes bundled with another product, it'll be proprietary. Companies just don't bundle products to increase your freedom or their competitors power.
That said, the apps on my TV are surprisingly serviceable. I can even stream video files directly to it (though an Apple TV does this with better reliability and video quality).
The only unforgivable failure is that it doesn't have a Twitch app, but neither does the Apple TV, XBox One, PS4 (it doesn't count if I can only watch PS4 games being streamed), or Wii U.
In 2 years it will be several more orders of magnitude worse than whatever new peripheral I have attached to my tvs, and they will have stopped updating the software on your tv because the hardware can't handle their little tv OS.
In which case, we could have the same regular updates you get with a roku.