UI Designer/Artist Benoit Perreault worked for Ubisoft from 2004 to March 2012. On his online portfolio - in the section showing his video game work and assets, he lists the three images I'm posting here.
The disclaimer NOT A GAME is ambiguous. The images could possibly be his own personal work, but I doubt it for the following reasons:
- The images are listed with his industry work, strongly suggesting they were a part of his career.
- The images list a specific format (XBLA, PSN (likely a misspelling of PNS)) - fan-art world have no reason to list a target format.
- He worked for Ubisoft for seven years and now works for Eidos. There is no reason I can fathom that he'd be creating Ubisoft fanart during his new career at Eidos.
- The images are located in a URL subdirectory called "Projects" alongside his other professional work - suggesting the game was a Ubisoft project at one point.
I have never played an Assassin's Creed game yet, so I'm not best placed to scrutinise the screenshots. It does seem to be a 2.5D fighter though.
The idea of playing other Ubisoft characters (Rabbids! Jade! Rayman!) is certainly quite appealing.