I was in the same dilemma on the 'toys' i wanted to work o my jap spec as well and had read all the alternatives to the solution and was gonna do the multimedia interface + reverse camera on the OEM screen + DVD player UNTIL i came to realization that i dont really need them. I decided to just put in the normal reverse sensor (with the beep beep sound) or use a camera with a separate foldable screen which i will open only when reversing. It's nifty so i don't see 2 screens and it opens up with a push of a button.
As for DVD it's mainly for my 3 year old so i got a iPad mount for the passenger head unit (darn good looking) and downloaded her movies/songs in there for her to watch. On long journeys plug in her headphones and i can listen to my music while she watches her show and we are all happy
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when she gets tired of watching her movies, she takes it down and plays with her apps.
All in i pay rm500 for the reverse camera thinghi and rm108 for the iPad mount instead of the rm3.5 to rm4k quoted to do the latter.