Sega originally planned to release Shenmue III, but over the years many have speculated that the game may never see the light of day. Various unconfirmed reasons for its delay include budget issues, poor sales of Shenmue II, and creative differences between Yu Suzuki and the more conservative management Sega installed after restructuring. Although Suzuki is still employed with Sega, he has not been involved in a major console title for years, and was not involved in the newer versions of series he pioneered, like Virtua Fighter 5.
Since the release of the second installment, Shenmue III has been announced for development and cancelled at least two times. Most recently in August 2005, when Kikizo.com revealed that Shenmue III would be a compilation of the first and second installments plus the final chapters. This, too, has apparently fallen by the wayside, as Kikizo later stated that Shenmue III is "worth forgetting about." After some time a new Shenmue project was underway, later revealed to be Shenmue Online. Despite an announcement declaring the project canned, series creator Yu Suzuki has expressed interest in reviving the project and assures its just in a "pending" state.
The entire storyline of the Shenmue saga is already finished, yet the final chapters (which would have made up its sequels) never went into production. And aside from some hidden leftover material, official concept art, and speculation it is unknown what the sequel would have been like, let alone how it could have ended. Fans petitioned for Shenmue III's development, which included a high profile (yet short lived) campaign issued by videoGaiden, but nothing official has been announced so far. Most recently, Suzuki was quoted as saying, "Regarding Shenmue 3, we're not carrying on relative development yet, and I can't give you any further information for the time being." Similarly, Simon Jeffery (President of Sega of America) was asked whether Sega was ever going to release Shenmue III, to which he responded "There are no plans for [Shenmue III] right now." And noted that it was "definitely one of the most requested fanboy games."
Despite all this, a sequel may still be possible because of continued massive fan demand, Suzuki's insistence that "the story will be finished through games", and SEGA's current trend of reviving old franchises.
Text from Wikipedia.org
See also ShenmueCampaign.org
See also Shenmue Dojo's speculations and research about Shenmue III