Assassin's Creed: Unity is definitely a thing, and it could bring horizontal wall-running into the mix, similar to Ubisoft's Prince of Persia franchise.
It follows this leaked still from what appears to be the next Assassin's Creed: Unity trailer. It shows a chap walking down a Parisian street.
Only running up walls is so '2013,' but it sounds like the squares at Ubisoft are getting with the program, according to professional parkour artist Jesse La Flair.
Posting in a YouTube video comment thread, La Flair teased, "What if I told you I may or may not have worked on the NEXT AC and they may or may not have added the ability to Horizontal Wall Run in the game."
We're treating this as rumour for now, but it's not a 'leap' (hurr!) to suggest that horizontal wall-running could be a feature in Unity.
We'll have more on the game as it comes. For now, marvel at the original Assassin's Creed: Unity trailer.