So, I recently rewatched the Pokemon Evolutions trailer again, and dropped it down to 0.25 speed and based on what I saw there, and the names of the episodes, I think I've got an idea on what they're going to be about.

Episode 1: The Champion: Galar.
Pretty obvious, as it's one of the main focuses of the trailer.  Battle against Eternatus, and then Championship battle against Leon. Male Protagonist.

Episode 2: The Eclipse: Alola.
Focuses on Ultra Moon with dealing with Lusamine and Dawn Wings Necrozma. Female USUM Protagonist.

Episode 3: The Visionary: Kalos.
Focusing on the battle against Lysandre and the Ultimate Weapon.  Male Protagonist with Xerneas.

Episode 4: The Plan: Unova.
Not much info on this one.  Poster shows BW Ghetsis with Zekrom, and scene shows Zekrom facing against Alder and Volcarona.  Possibly N's Castle?

Episode 5: The Rival: Sinnoh.
Focusing on Barry with Prinplup and Empoleon.  Scene shows him losing to Jupiter.  Potentially battle against Protagonist?

Episode 6: The Wish: Hoenn.
Focusing on Delta Episode with Zinnia and Rayquaza, as well as Sky Pillar.  Female ORAS Protagonist.

Episode 7: The Show: Johto.
Doesn't actually seem to focus on something that occurs in the game itself, but a show performed by the Kimono girls, telling the story of the two towers.

Episode 8: The Discovery: Kanto.
Doesn't really show much on it, but there was a brief image that may have been Cerulean Cave, so potentially battle against Mewtwo.  From the look of the poster, based on Let's Go, since it shows Green with Blastoise, which makes the battle against Mewtwo even more likely, since you first encounter her in Cerulean Cave.