Bummer that it's coming out in Fall of 2017. I hope it isn't equivalent to FarCry 4 where the previous game was so amazing and new that they can't really improve on it with the sequel so it's essentially a copy of the last game set in a slightly new environment.
The trailer was only a minute long but it doesn't look like it's taking place in the future. If I had to guess you're John Marston again but the young version when he was still in the thick of being an outlaw.
You probably have to get respect of all of the gang members until you're in the gang. Spend some time doing outlaw ****, realize it's not what you want to do, then fight your way out and leave, ultimately getting shot in the stomach. The game would end where RD1 began.
...or you get to be Bigfoot and go on a baby-eating rampage