I'm aware that I'm thinking waaaaaaaay ahead here, but it's just a thought.
Whenever making business decisions, the biggest concern is how much profit can be made from said game and the potential for a sequel. With Shenmue already having two games, I think that's where Sega's reluctance towards this game lies. Let's say Shenmue III does get greenlighted, will it be developed with the intention to end the saga? Or will it end to set up Shenmue IV? Hopefully it's the former and not the latter, because I don't think I can take another cliffhanger Shenmue ending.
But if the series does end with III, where does it go from there? Personally I think they should intertwine Ryo and throw him in with Kazuma Kiryu and create some kind of Shenmue/Yakuza hybrid game. It would give Sega some fresh material to work with. If Sega can put guns and zombies in the Yakuza universe, there's no reason at all Ryo can lend his hand and beat the shit out of thugs on the street like he's always done.