Ubisoft is on the verge of announcing a new Assassin's Creed title, but the studio has yet to reveal any specific details about the setting. Previous titles in the Assassin's Creed series of games took place in various parts of the Middle East, Italy, Turkey, and most recently in North America. The game's extended universe, which includes novels and comic books, has also seen the inclusion of Russia.
The studio has explicitly stated that it has no plans to set any Assassin's Creed title in Japan due to the fact that the order of Assassins are simply not the same as ninjas of Japanese history. Beyond that, any Assassin's Creed game taking place in Japan might invoke comparisons to other games, including Ninja Gaiden and Shinobi. Regardless, the omission of Japan as a possible setting does not rule out the Far East. Considering the inclusion of a Chinese character in Assassin's Creed 3's in-game encyclopedia, it isn't entirely out of the question that Assassin's Creed 4, or any future title may be set in China.
A Chinese setting wouldn't be a first for the series, given that Assassin's Creed: Embers covered the escape of a Chinese Assassin named Shao Jun, who seeks the help of Ezio Auditore to save the Assassin order in China. The film was released with special editions of Assassin's Creed: Revelations and the events of the story are heavily referred to in Assassin's Creed 3 (in the encyclopedia) as a major part of the series' canon. It would be no stretch to suggest that Ubisoft has developed the Chinese setting, which given a few extra details, would fit perfectly as a setting for the upcoming game. Additionally, the life of China's first Assassin, Li Tong, could be greatly expanded upon and serve as an even earlier ancestor to whomever the new protagonist is.
With the setting in mind, a Chinese artist named ChaoyuanXu has put together various pieces of concept artwork depicting a Chinese Assassin in ancient, 7th century China.
Given China's history and the incidence of high-profile and highly organized assassinations, there's little reason to think why the setting wouldn't be perfect for an Assassin's Creed game.