What do you think the setting of the next game will be (assuming it won't just follow up the events of the third with the same characters)? Personally, I think the key to picking the setting is choosing a time and civilization that's more advanced than that of the previous game, but not so close to modern times that the Assassins' methods become redundant with all new technology. Some locations like that could be:
- Late 19th century England
- The Western Front of World War I
- The European Front of World War II (such as Nazi Germany under siege)
Any other suggestions?