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
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.