So i've been seeing a lot of people thinking the scene in the trailer is the live-action version of the Rebels epilogue, but i don't think that’s the case (yet). Here's how i think it goes:

Sabine is on Lothal, like she thinks Ezra told her to. Ahsoka is looking for clues on Ezra's whereabouts because of the promise she made to him.

Ahsoka starts hearing whispers about Thrawn's return from the Unknown Regions, and goes to Sabine to tell her, as we've seen in the trailer. "Things have changed".

In this moment, Sabine is just there to protect Lothal. She’s not wearing armor, and her hair is grown, which could be an indicator of a "mourning period" of some sorts because of Ezra going away. She may even be skeptical about those rumors at first.

Another detail is Ahsoka's grey robes, instead of the white ones we see in the epilogue. Dave Filoni already said he loves comparing Ahsoka to Gandalf, and when talking about Ahsoka's timeline in the Mandalorian he said "Gandalf the White comes after Gandalf the Grey", just like Ahsoka the White comes after Ahsoka the Grey.

I believe after Ahsoka's first visit on Lothal, she goes through some sort of spiritual journey herself, letting go of her past traumas and using the white wizardy robes she wears at the epilogue.

Same goes for Sabine, understanding now she has to go after Ezra, ending her mourning period, symbolized by her cutting her hair and wearing armor again (we even saw a shot of her like that in the Ahsoka series during Celebration). That scene in the trailer where she’s kneeling in front of her helmet even seems to parallel a lot that scene where Kanan cuts his hair in front of his mask.

And then we have the Rebels epilogue with Ahsoka and Sabine going after Ezra and facing off against Thrawn, which i'm sure we will see it recreated in the series.