Original video located here. Accessed 21st October 2016
Well, like pretty much every teaser trailer ever made, this trailer doesn't say a lot about the game. It just has enough scenery shots and brand recognition to generate buzz. Sure Rockstar could do with the buzz but buzz won't mean a lot if there isn't a game to go with it.
At the present time, popular opinion suggests that this game will be a prequel and focus on John's days as a member of Dutch's outlaw gang. All I can say is that I hope this does turn out to be true as a) that's pretty much the only direction you can go with this sequel and b) with everyone favoring this option it would a disappointment not go down that path.