With the new information from the trailer, I can drop these leaks more securely without linking myself to them as easily.

- The three storylines are as follows:
-- Classic Gym Challenge
-- Treasure Hunt, involving exploring Paldea for artifacts/relics/phenomena related to the transformation/terastallization of Pokemon, extends into the traditional "post-game".
-- Evil team storyline involving militaristic research into Paradox Rifts.
- Jacq and Clavell are involved with the evil team, though neither one is the leader (think Faba from SM/USUM).
- Penny is the daughter of the Team Leader and often is absent from the academy due to her (involuntary) role in the research. She has the opposite legendary to your version (Miraidon in Scarlet, Koraidon in Violet). Effectively Lillie from SM/USUM if she had filled Gladion's role.
- Northeast section of the map (covered by clouds in the art) will be for post-game, connected to Kalos and the Treasure Hunt storyline.
- Central swirling cloud area (in the art) is connected to the Paradox Rifts and Evil Team storyline, and will be heavily involved in a new post-game mechanic, similar to Max Raid Dens and Ultra Wormholes, though focused instead on Paradox forms and some Pokemon from other regions.
- Treasure Hunt storyline heavily implies connections to other "crystal-based effects on Pokemon", i.e. Mega Evolution and Z-Moves. Unclear whether or not one or both will be included in the base game at this time.
- Nemona will "teach" the player different Pokeball "throw styles" as they progress. Explained by her "trouble throwing Pokeballs" at the start of the game. Allows for Player Animation customization.
- Arven will introduce the Pokemon Picnic mechanic and provide new recipes and ingredients as the player progresses.
- Koraidon/Miraidon will not start with all traversal abilities, instead gaining new forms/traversal methods at various key locations.
- Terastal mechanic only changes the Primary Type of the Pokemon.