User blog comment:Master Sima Yi/Assassinews 19-03-'14 – Two Assassin's Creeds for 2014?: Unity and Comet/@comment-187.38.115.3-20140611130036/@comment-3534734-20140612143136

They seem to be worried about the barrier of entry for new comers. Not having a number seems to imply that you don't need to have played the previous titles, at least for this one anyway.

Alex Amancio : "We are also using this opportunity to start afresh in-terms of narrative. Assassin's Creed is a very narratively driven brand. And any brand that starts dragging on the story for too long become a little bit complex. It's also a barrier for new fans. Assassin's Creed [Unity] is the beginning of a new cycle. Unity is really a new cycle."

https://www.youtube.com/watch?v=6XQl5J6iFuE#t=419