Looks like Formations are replacing the Pair Up mechanic? I guess different formations will give you different stat boosts. You can see them switch to an arrow formation at 1:33 of the trailer and the soldiers rush in. The stat boosts may become less effective if you lose these backup units. Feels a little Advance Wars-y.
Edelgard looks like she has the Vantage skill. The menu also shows an option for Combat Arts so they seem to be returning from Echoes.
Doesn't look like there's a weapon triangle.
Archers can counter at close range.
The red lines are enemies that are in range?
I wonder if the castle is going to be similar to My Castle from Fates and you can customise it and this is where you can interact with your units, which they show in the trailer.
Girl at the end looks like Tiki, but it's hard to tell for sure.
That trailers gonna get watched a lot between now and Spring.