In my opinion there are 2 important lessons that Ryo will fully learn in the story.
1. Keep friends, those you love, close to you... - Iwao Hazuki
2. Martial arts are used to protect people's lives, if you use your fists otherwise you will walk on the path of evil, too... - Xiuying
I always ask myself... how Ryo will fully learn this lessons? in my opinion is super important for the development of Ryo to fully learn this lessons.
Now i will imagine what can happen in the story for Ryo finally understand and learn this lessons.
The ending of Shenmue III showed that Ryo still want to kill Lan Di, he still want revenge but in my opinion this will change, i think that some day he will lose purpose and will forget about revenge, and i think that Ren will have big moments that it will show that deep down he have a kind heart, that Ryo changed him, that staying with Ryo made him realize that friendship is more important than treasures, that the real treasures are friends.
Maybe Ren will die saving Ryo, i don't think is a bad idea, i really feel that Ryo will learn this lessons in the hard way, some people only learn lessons in the hard way and i think that this will probably happen to Ryo, i think will be interesting and emotional if this happen.
At this moments i think Ryo will remember his father's words and Xiuying's words, i don't know if it will be in the same scene but i think he will remember Iwao's words and Xiuying's words, i think he will have a big character development, and in this moments he will fully learn this lessons, probably in a similar style when he remembered Xiuying's words before defeating Dou Niu,
Other important part of the story is how many moves are left for Ryo to learn in the story, in my opinion Ryo will continue to learn Akira moves - Bajiquan moves.
How do you think Ryo will fully learn this lessons about Iwao's words and Xiuying's words? how many moves Ryo will learn and what moves he will learn? it is a interesting subject.