@redimo, I have pretty much the same idea. Only in a rally car, because those are the best (just joking) and I prefer a solo car. Then again Solo I events are solo and on the track... Anyway, my idea is a NeoPixel ring and a 4-digit 7-segment LED display installed into the body of a standard guage.
Unless you have something out of the ordinary, your car will provide +12V at the OBD-2 port. I would assume it could supply plenty of current as the dashboard and the associated interior lighting are likely to be on the same circuit.
The Carloop has an onboard regulator to bring that down to +5V (1 A). I recommend using that +5V (VIN on the Photon) to power the NeoPixels. 144mA is the nominal current requirement and I expect would be no problem for the Carloop, but you might have to pay attention if you are also using a SD Card at the same time.
Note that it is recommended to use a capacitor on the wire supplying the power to the neopixels.
The output pin on the Photon will be 3.3V and it should be strong enough for the neopixel "input" line. However, if it turns out to not be strong enough, use the 3.3V to control a transistor that will drive it to 5V. You do not need a bi-directional converter as the signal is only needed one-way only.
In summary, you should have no problem at all doing this.