Yeah, I saw the same thing and was curious at the time, but couldn't really find any info.
I got my 300C a week ago and a good friend was impressed enough with the HEMI that he just bought a loaded Durango Limited. And it has the VES (Video Enteratainment System, I think), which is the rear seat DVD player. It really works pretty nice. My assumption is that one of these could tap into the head unit on the 300C in the same way (but no, you won't be able to watch DVD's on the NAV screen).
I'm planning on asking my dealer if they can install one of these in my 300C. I'll keep you posted.