back on topic... my ideal car dvr setup would be something like this:
replace the entire rearview mirror with one that has something like a 4" touchscreen in it, maybe running android just for the flexibility this offers. NO cameras built into the mirror itself, but GPS could be optionally built into it. have the cameras (at least 2x 1080p) mount remotely and run their leads back to the mirror. the cameras themselves would be very small so they can be easily concealed. i would mount one just below the rearview mirror's mount on the windshield, and another in the center brake light in the back window (if it's at the top of the window), or maybe use a factory-style backup camera (but higher resolution) that can be externally mounted so that it can be used as a backup camera. theoretically you could include 720p pinhole style cameras on each end of the mirror itself to provide view out the driver and passenger windows. there would have to be some way to aim these though, since LHD and RHD cars would have the mirror mounted at different angles, in addition to the angle each driver personally sets the mirror.
using android on the main unit would give so much more flexibility in terms of configuring the device, as well as playback, since it would be a good-sized screen and as long as someone wrote a good UI for it, it would be a piece of cake to operate. you could even load things like
OSMAnd to have GPS navigation without needing an internet connection. If the device were made with two microSD card slots, you could have one dedicated to DVR storage, and the other full of music, which could link to your stereo via AUX or bluetooth and have controls/display right on your mirror.
having the mirror be the brains and display would be quite stealthy, especially if there weren't big lenses and things sticking out of the mirror. my main complaint about the rearview mirror DVR that someone was piloting here recently is that the camera sticking out the back was huge. it would get knocked out of aim every time i put up or take down the sunshade in my windshield while parked. having the cameras be separate is not only more discrete, it's more reliable since they're less likely to be bumped out of proper alignment.