Más leaks... Cuando me refería a una revolución en Pokémon me refería a esto, esto sí que pinta más a por lo que yo estaría dispuesto a pagar, ojalá se cumpla:
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.
I can confirm that there will be 2 versions: Pikachu and Eevee. In addition to choosing a traditional fire/water/grass starters, Professor Mulberry will also give you a Pikachu or an Eevee depending on the version of the game you are playing.
Following Pokemon is back, KIND OF... If you're playing Pikachu version, then Pikachu will follow you. If you're playing Eevee version, then Eevee follows you.
When Eevee evolves, the Eeveelution will follow you (and yes there is a new one). Pikachu doesn't evolve, but its stats scale differently than a Pikachu caught in the wild. Follower Pikachu is comparable to a fully-evolved starter by the time it reaches level 40.
THE SCREENSHOT with the Lapras and following Eevee is a total fake, the real graphics are a small-to-medium step up from that and the overworld camera angle is different from the 3DS games. However, it hints at a lot of real info. It's possible that someone else on the team made that screenshot to leak without getting caught? If so, it worked!
ULTRA SHINY is not a thing, as far as I know. If there have been any mechanic changes to shinies, it is not mentioned in any of the scripts they sent over for localization.
Gyms are back. Poke Ride is back, there's no HMs.
The rumor about a Snake legendary is FALSE. I have not seen one. This game's Mewtwo/Arceus is a very cool Poison-type Spider Pokemon. I wish I could say more but I've already said too much.
Some other things I'd like to mention/clarify.
Yes, Red and Blue ARE in the game. As OP said, there's "Nostalgic flashbacks" to old Kanto. That's where you see them.
Pokemon Go integration is a thing, but it's not really as severe as you might think. You can complete the game without ever using it, but you won't be able to complete the Pokedex without it unless you trade. There's also a special currency that comes from Pokemon Go integration that can be used to purchase certain items like TMs and whatnot.
The game is essentially a reboot. Like, it's not called a reboot, but it more or less feels like one. The majority of Pokemon will just outright not exist anymore in the game's data. There are 151 old Pokemon (and not all of them are gen 1 Pokemon), and 100 new Pokemon. However there will be a number of alternate formes that can be obtained for a whole bunch of Pokemon. The "Alolan" forms are the new standard, but now they're considered the "normal" forms and the classic ones are now dubbed "Legacy" forms. For example, "Alolan" Vulpix is now just Vulpix, and Legacy Vulpix is the original fire type.
As OP said, you can catch Legacy Forms in the alternate world. And this is not something that you need to reach the endgame to do. The alternate world is available fairly early on, and you can even obtain Legacy Pokemon even earlier via Pokemon Go transfers.
The game is kinda-sorta open world. You can complete the Gyms in any order provided you can reach them, and there are tons of different ways to make your way around the world via different Ride Pokemon. The Gyms will get stronger depending on how many Badges you have.
Catching works differently now. When you throw a Pokeball, it will ALWAYS catch if it connects with the Pokemon. However they will now try and dodge the Pokeball or knock it back at you. By reducing their HP or giving them status ailments, you'll make it harder for them to react to your throws. The concept of "Great Balls", "Ultra Balls" etc is now gone, in that there is no outright better ball other than the Master Ball, but different balls work better in different situations.
