Interesting I'll have to check this out.FYI, if you want to watch a good history of that time in Japan, I suggest "Age of Samurai" on Netflix. It's a docuseries and shows how Tokugawa Ieyasu (the real life Toranaga) came to power, starting with the rulers etc before him how they came about, and eventually how he rose to become Shogun.
Had I not remembered the Chamberlain series also ended like this I would have expected season 2. I was OK with the ending except I do not really like when the characters have to spell out verbally what just happened and what is about to happen like Toronaga did when he was seconding the traitors head off there at the end.The next to last episode should have been the ending because the last episode felt more like the ending credits where they do where are they now or what happened to them summary.