If anything the Chinese armours and weapons fit more in the game than the Japanese stuff does. The Chinese weapons through a LONG era are focused around spears, bows, crossbows, dagger-axes (second polearm from top in pictures above), piercing swords and heavy cutting swords, very much of it suited for fighting armoured opponents, and many of their armours can already be found in the existing Khergit-style lamellar and mail armours in the game.
Hell, the Khergits (i.e. base game-content) are Mongol (The Golden Horde), so even if the environment setting isn't China-fitting, the step from Golden Horde to several eras/reigns/kingdoms in All Under Heaven isn't big at all.
Some very nice stuff in those pictures there, even though some I can be without (the fantasy-looking or ceremonial stuff).