I would love it if Ryo Hazuki would make it to the game. But it doesn't make sense at all; Ryo will have to be properly aged (Shenmue is based in the 80's), he will have to have developed more of his other chinese martial arts along his journey, and he would have a different personality because that's what's expected in the Shenmue story. Ryo is a character that's in his infancy in development. We only saw up until Shenmue 2; while Yu Suzuki has written the story up to 11 chapters so far. As a Shenmue fan, I think you need to at least have to consider these things if you want the Hazuki fans to cheer for a cameo. Otherwise, he wouldn't be interesting to the fans (IMO) and he wouldn't be interesting to non-fans in the first place.
I really hate reading this crap... They are just guest characters, why do they need to "make sense" ?
Did link make sense in SC2?
Did spawn make sense in SC2?
Did Heihachi make sense in SC2?
Did Kratos make sense in SC:BD?
Did the Star Wars characters make sense in SC4?
Did Kratos make sense in MK9?
Did Spartan make sense in DoA4?
Seriously...Why does it matter? It's like people thinking Leon and Ein need to be part of the story somehow to be in the game.