It's March, which means we will probably get an announcement/more information soon, whether Ubisoft wants it or not (based on past history)
In December it was leaked that the next game, codenamed Victory, would be set in Victorian London. Beyond that we don't know much, but the leak came with several pictures, and Ubisoft later confirmed the game.
Spoiler Alert, click show to read:
The only other thing we really know is that Ubisoft Montreal (the lead studio for every game besides Liberation and Rogue) is not the lead this time, with production mainly being done by Ubisoft Quebec.
Article from December
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For what it's worth, though, I think that Ubisoft's main problem concerning Unity comes from upper management, not on the dev teams. The dev teams clearly put a lot of effort into making the game, but I think they were simply pushed towards unrealistic goals. My hopes are that Ubisoft takes the criticisms of Unity seriously. Whether it was the bad story or the performance problems, Unity definitely was one of the worst games.
Other than that, I am glad we get to see Victorian London, but I do hope that we soon get a game set in another locale, besides the upcoming Assassin's Creed Chronicles: China.