I think there's a possibility.
Shenmue is said to have 13 "chapters."
If Sega is still taking that route, I hightly doubt they would release all of them on Xbox, since they would want to reach a broader audience...(remember that though Shenmue was a great game, it didn't sell the way games of that caliber should).
However, if M$ decides the throw tons of money at Sega to keep Shenmue exclusive....
Seeing what happened to the RE series, MS may be compelled to do that.