Well fuck me.
Ubisoft are not replacing Desmond Miles. They are doing away with the modern storyline altogether, more or less, because Ubisoft don’t want to “make you” play through a present day character.
Even though that was, you know, the really fucking cool thing that set Assassin’s Creed apart from other historical games.
"The present day in ACIV is basically the logical continuation of the ACIII present day. But this time, instead of making you play through a character of the past through a character in the present, we wanted to make it even more immersive for the player, make it more fun. So, you are now a full-time employee of Abstergo Entertainment, and you’ve been hired there as a researcher. You are the one in the Animus doing the research on an important character from the past, Edward Kenway.”