I will mostly confirm and debunk and clarify on some of the most-talked about rumors, since I am less likely to get caught that way. I will also attempt to leak some new information I believe to be safe.

I'm not using a tripcode. I don't even want to be tempted to reveal my identity. I understand if you don't believe me, I only ask that you hear me out.

I can confirm that it is Kanto 100 years after Gen I. It is much different from the Kanto you remember. There's a mixture of new Pokemon and returning Pokemon. Returning Gen I Pokemon have new designs and even typings in some cases. Some Alolan forms return instead of the original.

There are nostalgic flashbacks to the old Kanto hidden throughout the world. It's a little like Zelda's Memories in BOTW. They are hard to find, but they open up small zones where you can catch the original versions of returning Pokemon.

Overall there is a lot less emphasis on plot than in the previous games. The new team (not gonna say the name) is incompetent but wealthy. They are responsible for a disaster that changed the region.

I don't know where the Johto and Unova rumors came from. If these regions are in the game, no one in the NA localization team knows about it.