Plus, AI and you just can choose "support" the shogun but plot to kick him out of his seat. Or just use the situation to "help" the shogun but actually expand your domains. useful if you are a small clan and need protection from the beast like Hosokawa, Yamana, and Uesugi.
It is also useful for the onin war scenario where the warlords actually take side in the war.
There is another victory that you can take. For example, the retinue victory, or honorable victory. With this, you can take side of a shogun, support him to the end, help him to rule over Japan and become the most honorable samurai of Japan. You won't get land, maybe the shogun will give you some. But, you won't get many of it. Instead, you will get loyalty point or honor point or something that bring your character to a status of "the loyal retainer who help the Shogun to bring the peace to the land".
With this, both AI and you can pursue this kind of victory. That's why, you will find an AI that will help you like a die hard supporter if you are the shogun (but of course, not many)
I know that it will require a lot of coding though. But I also know that Paradox has a lot of experience with that kind of features.
