Like an Iroquoian nation will form the Iroquois if they are first to pass the Federal Constitution reform. I think it would be cool, even if possibly generalizing significantly, for native tags to form unique and powerful federated tribes with unique ideas and missions that help them to establish a power base in their local region. I would therefore limit it to one specific formable tag per culture group. At the moment I think that the natives feel rather lackluster, and I think having unique and interesting formable nations would possibly give people more incentive to play as them.