I'd love for each purchase (or perhaps perchase group) to be able to upgrade users separately. For example, my company sells a physical book and when you buy it, you get a PDF copy too. We do plan on making more books, so adding everyone to the "I bought the book" group won't work for multiple books. So I'd really like to be able to map usergroup promotions to purchases so that Book A buyers get promoted to a usergroup that gives access to a download of Book A while Book B buyers get promoted to a usergroup that gives access to a PDF copy of Book B.