You are correct, there is no way to import revision history into another Booktype instance at the moment. The only way how this would be possible is to make up new format where we would export all needed information (user info, book info, chapter info, revision info) for another instance. On the other instance we would import correct user information (create new user if needed), create book, import correct revision info and etc.
There was a plan to do this. It would be used also as a good backup solution for users because they would also get entire book revision if they want.
Some earlier version or predecessor of Booki/Booktype apparently had a list of contributors as Dublin Core metadata. And this metadata still remains in the older books.
Current version of Booktype doesn't add contributor metadata though? Can you re-enable this? Currently it seems to only add creator metadata?
And maybe enable the editing of this metadata in the book editor? It would make it easier to handle the contributors list when you move the books around.