first of all those guys at 2:55 look like temple guards, We last saw them in the Clone Wars, they're jedi's highly trained as protectors of the order
Ok, as to the lot we've seen.
We clearly see Ashoka having a vision of Anakin that confirms that she knows or has found out the truth about Anakin. We also see her showing Ezra a holo recording of Anakin in action.
We see Ezra talking with Yoda, he's had a vision of this before, we also see Ezra picking up what looks like a Sith Holocron. its clear that he's trying to find out more about the Darkside of the Force. He also is seen standing by a Sith Obelisk, its possible that he found a Sith Temple. Its seems to be coming down to his desire to become a jedi in season one when Yoda asked him why he wanted to become a Jedi? He wanted to become powerful, protect his friends and fight the Empire. He's having a similar discussion with Yoda in the trailor where he basically says, he wants to fight, and Yoda asks him the how question.
We know Ezra has felt the pull of the Dark Side before and used it, and he has recently learned that his parents are dead thanks to the Empire.
The old master has some familiar face markings, I had wondered what happened to him at the end of Clone Wars.
I think that we're going to see a split, the Jedi, fresh off the betrayal of the chosen one, might not want to take the chance that Ezra will betray the light side of the force as well.
We might see Ashoka facing her destiny as she confronts her old master. (BTW I loved the visual of her with the tear rolling down her face as she sees Vader on the ship
We finally see Hera's father, who had a major role in a couple of Story arcs and novels from the Clone Wars era.
Overall this looks really exciting