The problem with your suggestion is that, for people like me who don't care that much about minion collecting, if I win the minion I can no longer put it on the marketboard for someone else to get instead nor give it away, all that suggestion really does is enforce usage of it. Minion drops are already rare as is, and there are plenty of people who get absolute fodder loot rolls, me included. At that point why even bother making anything registerable marketable?