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1. They're downplaying the secret identity factor of the registration act and upplaying the vigilante aspect of it. This makes a lot of sense since there arent many secret identities in the MCU.
2. Black Panther's costume looks awesome.
3. Ant Man isn't in the first trailer but I think I saw him on the poster so his part must be a lesser one.
4. I was really hoping to see Daredevil in this and to really make a connection between the MCU and MNU. You can always have Murdock as a lawyer for some bill meetings or whatever.
5. I like seeing General Ross in there and hoping it will eventually lead to a Red Hulk. That's just wishful thinking but it would be cool to see Banner on a planet hulk storyline and at the same time a Red Hulk taking his place on the Avengers post Civil War
6. Big focus on both Bucky and Falcon in the trailer, makes me wonder for future movies who will take the Cap mantle after Rogers. comic spoilers:
Spoiler...Bucky took it after the Comic Civil War story and Falcon holds it currently in the Marvel universe.
I think they've been planning on doing a Civil War story for a while because it was huge in the comics not just in taking up space but for setting a tone of the Marvel Universe in a post-9/11 world. However, I think you're right in that they pushed it out for next year to compete with BvS. I bet a good portion of it comes down to contracts like Downey saying he doesn't want to make any more movies as Iron Man (which is a dumb idea IMO) so they made sure to make the Civil War story that NEEDS both Cap and Iron Man while Downey was still on board.