Did that trailer yesterday excite you?
Well it excited me too, because now I can leak this without the bosses finding out how I am.
It's not made explicit exactly how long after XY the game takes place, but it's said that the player character was a baby when Team Flare reactivated the Ultimate Weapon. It's also implied to take place shortly after The Hidden Treasure of Area Zero because Jett mentions "recent discoveries in the Paldea region by Blueberry Academy"
Clemont works for Quasartico as an engineer and Bonnie has taken over as the gym leader.
Shauna, Trevor, and Tierno have all achieved their goals but they're getting bored with life and there are sidequests involving helping them spice things up.
Sycamore, Sina, and Dexio are working on the redevelopment project
Looker is investigating Quasartico because he believes there is a conspiracy among some employees to restart Team Flare. Jett isn't a twist villain but there are a lot of red herrings.
Emma has become the mayor of Lumiose City.
Steven Stone is now the president of the Devon Corporation, which purchased bonds to finance Quasartico's redevelopment plan.
Korrina introduces the player and rival to Mega Evolution
Zinnia shows up in the postgame, you'll have to wait and see what that plotline is. It involves Rayquaza.