For me, getting this particular person on the project is like trying to make a movie and having, say, Kathleen Turner phone up and say "Are you looking for any actresses?"
So now we're getting into the nitty-gritty work of it, and the Mysterious Unnamed Collaborator is sending me materials, and they're great stuff. :) Not like they'd be anything else -- but seeing the actual great stuff instead of just thinking about how great M.U.C.'s stuff will be, still makes me pump my fist in the air and go, "Yes!!!"
Look for an announcement next week, at AnthroCon if not before. Prepare to be amazed. ;)