It could also be intentional. This happens every year thus far since the AC3 (maybe earlier)

http://gamespace.daemon-tools.cc/eng/news/picture-of-assassins-creed-5-hero-and-new-assassins-creed-4-black-flag-edition-have-appeared-in-the-network-2014-03-11

What do you think? What setting will the game take place in?

According to speculation and the poster it appears to be new, and he's sporting a revolver.

I was originally going to suggest Wild West (plenty of revolvers there), but the clothes don't match. Everyone seems on board with Victorian England. I won't dis-believe that until proven otherwise. Either way, it could easily be in the mid to late 1800's.

It kind of looks like the character is giving the middle finger in that photo. :p

Are you sure it's a revolver? Zoom in to the picture, it seems like it's sticking out from behind his fist, not held in his hand. It also appears to come to a point, more like a blade.

ETA image:

It doesn't look like a gun in his hand to be honest, and if it is that's a weird shape for his hand to hold it. The object juts out from between two fingers. Another thing to note is that it looks like he's wearing a metal chest-plate. The most curious thing of all however is the color: The iconic, classic white cloak is now a dark black hood and cloak. What any of this means I've no idea. But another thing to keep in mind is that there's no reason they couldn't look backwards instead of forwards in the respective timeline of their games.

If they are going for the standard dark, sooty, Victorian England setting (steam punk maybe?) then white would stick out like a sore thumb, even more so than any previous settings. It does make sense from a story POV for an assassin in such an environment to wear black. From a franchise point of view it would be a significant departure.

This is all a big if. Like you say, we don't really know where or when it's set.

Then again, Ubisoft has also been doing surveys that say that the general public wants more games to be treated somewhat more separately from the Assassin's Creed name, in particular more installments similar to 4 as strictly pirate games. What we could be seeing may just be a spin-off sequel of AC4

Victorian England would actually get me to pay attention to this series again.

Assassin's Creed is a yearly series. Ubisoft will run it into the ground until it's dead, then rinse and repeat with some other IP. The lack of a fixed time period for the plot means it might take longer for this process to reach its inevitable conclusion.

I've played every single console release of Assassins Creed since the first game. I still love them, even if the gameplay is recycled. It's like a cinematic movie series, going for years, with sequel after sequel. I get attached to the characters (or develop distaste for them), but regardless of my feelings for them, the settings and the immersion into those is what keeps bringing me back.

The site I originally found the article kept mentioning revolvers in the comments and in the article itself, so I was just mentioning speculation as to what was in his hand. I'm not sure myself.

The clothes don't look wild west to me though, but I can't be sure on that either.

I'd like to see lots of settings. There are many other European settings that could work like England or even Spain, or even Latin America and have conquistadors, while you play a Mayan or Aztec assassin, or maybe oceanic islands in the pacific during times of discovery, or something entirely different. Overall though each new iteration has a new feel to it. Assassins Creed 2 had large city scapes and horse travel. Assasins Creed 3 had an enormously large countryside, with relatively smaller cities in comparison to Renaissance Italy. Assasins Creed 4 was mostly ocean and islands, with moderately sized cities, but lots of little towns and outposts, with lots of ocean travel by ship. I can only guess that five will experiment with something new, now that they've got the whole wilderness and wild blue sea aspects in the history books. Victorian England could feel like Dishonored, so they'd have to have their own unique take on it to make it feel new and fresh. The wild west could feel like Red Dead Redemption, so they'd have to be careful about that too. Either way I think we could be looking a setting during the Industrial revolution, or I could be thrown for a loop and we could go back in time to something far more ancient. Who knows! But the settings are the driving force behind the games for me, and I love them for re-creating historical places.

They did admit though that this next game has new gameplay and controls and is a big departure from past games in how you fight.