Current Wagn (1.7 tomorrow) doesn't version cardtype at all, but we really want to version it as part of the Content.  There is nothing really special about cardtypes, they are cards, every card must have a type, and the type can change with the content.  The set logic that is used throughout the API and in all Wagneering can use the type in specifying the sets for views, triggers, setting and the like, but otherwise it is just a card.