Hmmm, haven't played too many games set in steampunk floating cities, sounds pretty unique to me. Irrational is an amazing developer, and I have full faith in their abilities to craft an original and innovative experience that blends political philosophy with action-packed gameplay in an incredible location. The fact that the game is so much more open than the original Bioshock and is running on a completely new engine intrigues me as well. I like that they're actually having established characters this time around that you interact with directly, and playing as a Pinkerton agent seems pretty sweet as well. Then there will be plasmid like powers, flying around on rails, dozens more weapons according to Ken Levine, and upwards of 15 enemies coming at you at once? Consider me interested.
Oh, and another thing, setting the game in 1912 makes a ton of sense. While a floating city during this time is way beyond reality, it wouldn't really work at any later time with the story they created because of the advancement of technology. Since the story involves the city disappearing into the sky because it's a heavily armed "death star", the time period must be before airplanes really took off in a military capacity. A floating hot air balloon city would be a ridiculously easy target for attack aircraft.
Also, the name of the game. To me, it seems like using the name "Bioshock" for the game definitely connects it directly to the previous games. Since nearly any other name could be chosen to reflect spiritual succession (ie. System Shock to Bioshock) I'm betting Infinite will have something to do with the origin of Rapture. My reasoning for this comes from a specific spot in the trailer where there's that huge propaganda sign that says "Burden not Columbia with your chaff..." (I believe?) and shows what I'm guessing is a poor destitute baby being offered up to a woman who is a representation of the American exceptionalism theme reflected in the city of Columbia. The fact that she is shunning the poor baby while cradling a rich looking baby in her arms reminds me of the whole "The strong shall not be contained by the weak" idea in Rapture in the first game.
This makes me think that Andrew Ryan will be involved in some way, as if he was maybe a child living in Columbia and saw the downfall of it firsthand. The player character possibly has a hand in his escape during the end of the game, and Ryan sets out during the course of his life to build a city that would not fail in the same way Columbia failed. I.E. instead of grand fanfair and devotion to a country, a secretive city based on individualism.
