i have gone a slightly different way - i tried to preserve the factory look, functionality, and reversability...
parts used -
OE TV module (for US cars the TV module was never installed) ($150-300)
OE AUX input ($5-60)
car already came with factory Nav and factory PDC
aftermarket parts used -
rear camera ($20)
TV-in-motion module ($100)
BT-to-3.5mm adapter ($10)
MHL converter (to HDMI output) ($10)
HDMI-to-RCA converter ($30)
brain used -
any smart phone with MHL ability ($300-900)
added OE factory TV tuner, wired AUX input, connected aftermarket TV-in-motion module. these items gave me stereo audio input, industry standard RCA-style audio/visual input, dedicated reverse camera input, ability to run AV on main screen while in motion.
wired reverse camera via dedicated inputs, setup trigger to activate camera input upon PDC activation - gained manual ability to operate rear camera via button in front, or automatic operation via PDC
setup MHL converter from Android phone to take phone screen to HDMI output, converted HDMI signal into RCA signal, fed the RCA signal to AV input (original setup was wireless, gave up on that, went with wired), received the video screen from the phone on the main monitor...
connected BT-to-3.5mm jack adapter to the AUX input of the radio, paired BT to the phone.
as i get in the car, i connect the phone to the MHL cable (working on wiring up the cradle, so i will just drop phone into cradle), the phone automatically connects to the BT unit (once the cradle is finished, it will automatically connect to MHL)
as I drive, the main radio is in over the air mode, receiving local stations, or playing CDs... I press mode, until i get the AUX, then I press clock symbol (my tv-in-motion module uses the clock symbol to bring TV onto the main screen), and select AV from the channels presented (in USA only AV is available).
at this point I have streaming music from my phone via the car's stereo system, and the image from the phone screen on main screen.
drawback - the main screen is NOT touchscreen, so i still have to use the phone for navigation through icons...
this drawback can be mitigated with MIMICSX2 device - a BT digitizer for iPhone/android... i have not tested the device...
https://www.youtube.com/watch?v=R94c3kzF_wQ