That's an interesting idea, but I bet you will find the resolution of your Sony color monitor will not be as usable as you think. (TBD)
It's also a challenge to find a Sony adapter so you can connect your video out of your GPS to the back Sony-Video-In connector, which is a 6-Pin-Sony connector no one but Sony used... back in the day!
Has anyone every bought an adapter to RCA style video connector? (See picture.) Is there another source?
If these adapters exist, then I suppose you could also wire up a passenger side blind spot camera? (TBD) ...but you will still have to manually switch the display to the "B" or "C" to view the input video signal. This also means your Sony display will not split the screen for 2 or 4 quadrants like more modern back-up camera offer.
Replacing the Sony camera is no easy feat either! But if anyone has a more modern solution, I would love to know about it!
Here's a very helpful link to how John upgraded his Sony Camera to a Voyager, but I'm hoping there are other options now available?
http://janeandjohn.org/pages/BackupCamMonitor1.html
I can tell you this: If my Sony camera ever failed I would seriously consider taking it out, and install a Galaxy Tab A (10.1"), to cover the hole in the dash; and I would look into adding security camera options. (Pie in the sky type stuff.)
Good luck and keep us posted.