The main Question is: "Why Ryo and Shenhua get the sword?"
Will Ryo fight with this sword against Lan Di in the big fight in the end? Will Ryo kill the "chinese dragon monster" with the sword? Or ist the sword another key for something in Shenmue III or Shenmue IV?
In my optionen, we will learn the secrets of the sword and the two mirrors in the end of Shenmue III. In the end of Shenmue IV, Lan Di gets the phoenix-mirror and will do something very bad and in the last game, we defeat Lan Di.
If Shenmue III is ja commercial failure, YS will end the Series with Shenmue IV and a short version of the last parts. If the next Game is a success, then Sega will produce Shenmue IV and Shenmue V in the end.
But I also believe, that part III doensn´t have much fantasy content like the end of Shenmue II in the next game. I like Shenmue II more then the first game, but the last scene with Ryo and his friends learn about the backstory of the fathers of Lan Di and Ryo was a better ending then the mystic end in the cave with the sword. I love the part with Shenhua and Ryo in Gulin, but the end of the Game wasn´t a great cliffhanger, like the Information about Iowa Hauzuki. Maybe the story is true, mabe not. But that creats entsion for the next Game. More like a mystic flying sword and Ryo und Shenhua in a cave for the next 15 years ;)