David-
I believe you have just described Wikinfo, Fred Bauder's fork of Wikipedia. That is, it's already been done.
Wikinfo is an example, yes, although they do the keeping-in-sync part manually. I actually wrote a little script that makes the merging of Wikinfo and Wikipedia articles easier a while ago, not sure if anyone uses it. In the long term, I want multiple such forks with specific purposes (views) and I want to facilitate the cooperation between these different variants of our content. Mav's concerns about doing this within Wikimedia are understandable, but false. I will prove this when the time comes.
Regards,
Erik