So, returning to my leaving, one thing that was built into classical ryu was turning your student's loose. Musha shugyo - the teacher feels the student chafing, and sends him out to meet the world, test his techniques and to return when seasoned. At which point, he is either called a failure or a menkyo. And sent on his way, in most cases. In other words, built into the system was a rite of passage, like a father saying to his son, "you are a man in my eyes. I will always be your father, but we are now eye-to-eye, and that's how we will communicate."
I am in the middle of a critical review of the book. (Today, I received a new Japanese edition of the 兵法秘伝書. There is a fair amount of discussion in Japanese on the book and the author.)
One question. Do you think that Morihei Ueshiba saw his relationship with Kisshomaru in the same terms as you set out above? Of course, we know that aikido is not a koryu, but it does not follow from this that Morihei did not see succession, even family succession, in similar terms. If he did, I think this would explain quite a lot. The 'task' that Morihei set Kisshomaru was to keep the Tokyo Dojo running--at all costs.