Terry,
My initial idea is to explain exactly what Darwin is saying. The reason is simple - there are a lot of people (mostly, but not exclusively creationists) who believe they know what it says, but do not. I would like to summarize the most important points of what it actually says.

If this works out, I might even try doing a similar thing for other great works of science. I'm not sure.

However, I do have a mind that after the initial project is completed that I/we might include extensive expository material to update, clarify, etc.

Anything you might provide could be useful.
thanks,
(but also consider doing a chapter!)