Has anyone been following the progress of the AutoPi project?
https://www.autopi.io/how-it-works
Basically, it's a Raspberry Pi computer packaged into an OBDII dongle, plus software that allows easily configuring it to do car-related tasks, or developing your own extensions to it.
Their Facebook page says they're shooting for releasing it later this summer.
I'm thinking this would be a really cool way to add features without any modification of a "Tech" 370Z dash using a factory nav screen. Just output the AutoPi to the AUX audio and video composite inputs and buy something like a NavTool to enable viewing the AUX display while driving.
They're talking about AutoPi even having potential to add things like blind spot warning detection with the use of sensors on the car plus the right software extension.