Hi Ben,
Yes, you can do this with a 5NF XML data schema. You shouldn't do it with namespaces. That'll require code and may not work. You can do it with one namespace by just having a very normalized data schema. We've done it before. Makes the designer view huge (lots of conditional hide-show), but it works and is actually pretty cool. Send me email if you have specific quesitons (I'm only in the forum twice a week).
Good luck!