Location and era wise. Personally I'd love to see a French Revolution AC, and that could easily been done. A Feudal Japan would be nice as well. And maybe even a Russian Revolution?
I don't really know actually, the only thing I do know I want, is a more interesting locations and a bigger focus on assassinating important people, AC3's locations were horrible and the stealth even more horrible, the frontier was ok, but the cities were boring, I think Japan could be good in terms of location, I don't know about the story though, I heard people saying feudal japen earlier, can you explain to me what happened in that time period, because I have no clue xD
Russian Revolution was already done, in comic book form.
Like I have said elsewhere, Feudal Japan would be beautiful. I don't have much of an idea about significant events during the period, but I doubt there was anything less significant than the events of AC2 or Revelations.
Definitely no revolutions please. AC3 was too "America is the best!" to be enjoyable on my end. I have said this before, Johngie as my witness. A French Revolution may get that going with France. Feudal Japan all the way. French Revolution was my close second too, but only if they can make it more foreign friendly.