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Don't want to post too many details, in case it would become deleted, or too much stuff would be spoiled for people.
First brief announcement of Gen 8 is coming VERY soon, with more details to follow in early April.
The new game has an open world structure - with 18 gyms (these are back) scattered around the world. Player just need to beat 8 of those to earn the right to fight in the Pokemon Leauge.
The other 10 as well as the one the player has choosen can be battled again in the postgame. Also every Gym has a special, Challenge Mode with new traps and certain special rules (Weather, Trick Room) applying instead of being just a single type Gym.
To fight a leader in regulard game player needs to perform specific task for the leaders (kinda like in the Totem Challenges in S/M, but more ellaborate).
The story is STILL there, player has a remote TV device that informs them about what's happening around the world, or allows them to "watch" short shows.