Kotaku, the game will take place in the Victorian era, which makes some sense of the reported codename for the next rooftop-leaping game, "Victory."
Expected to launch in fall 2015, Victory will seemingly be the first game in the series developed by Ubisoft Quebec, the studio named as the lead of the game by the publisher in July. The report also notes that Victory will be the only Assassin's Creed game to launch next year, and is not planned for previous-generation systems (PlayStation 3, Xbox 360). We've reached out to Ubisoft for comment, and will update as we learn more.
Update: Ubisoft has confirmed the leak, offering the following comment:
"It is always unfortunate when internal assets, not intended for public consumption, are leaked. And, while we certainly welcome anticipation for all of our upcoming titles, we're disappointed for our fans, and our development team, that this conceptual asset is now public. The team in our Quebec studio has been hard at work on the particular game in question for the past few years, and we're excited to officially unveil what the studio has been working on at a later date. In the meantime, our number one priority is enhancing the experience of Assassin's Creed Unity for players."