If you ask FCA engineering, they will tell you it’s impossible to add ANY feature after the fact.
Well, we all know here that's nonsense! I figured the VSIM was a matter of too many wiring harness changes (which you've addressed) and too many system updates for FCA to be comfortable with dealers doing. To an extent, they do have a point–service departments regardless of brand often leave something to be desired.
When the hardware for this becomes available, I'll probably give a go at some kind of integration. I expect the "controller" is taking care of compositing the four video channels, and sending the result upstream.
Even without proper vehicle support, I'd think there are viable approaches. Just need to spend some quality time sniffing the bus on a fully configured vehicle, perhaps a bit of firmware on a microcontroller to wake up the controller, and inserting the resultant composited image through existing means. If we're really lucky, even that might not be necessary and it's just a dumb box that's not listening for anything. Just a matter of video or datastream switching then.
I think I have my truck project for next year