All of the OP's ideas are derivative and have become boring, and to be honest, I don't think much of Assassin's Creed (which I always think of as Ass Creed). I reckon that you could make a very good steampunk-style open-world game as long as you didn't go too overboard with the steampunk genre, as long as you didn't just make it a modern story which happened to have the style of the Victorian era.
And what about the modern era? Almost everybody ignores the sheer number of effective scenarios that could be done interestingly with an analogue of the real world. As for derivative settings of my own, the Wild West and post-apocalyptic settings could make very effective open-world games if you did them right.