That particular rumour seems to be developing quite a credibility, since it mentioned Sirfetch'd. Among other things the rumour had mentioned are Team Yell, Bede and Marnie, along with Camping.
(Text highlighted in dark purple means that it's confirmed)
Your rival is named Hop, but you will also be facing of against Bede and Marnie
Team Yell is the gang in this game, who are well meaning fans of Marnie causing trouble
To become part of the gym challenge, you will have to get an endorsement. Bede gets an endorsement from Chairman Rose and his secretary Oleana
Eternatus is the evil legendary. The other legendary will be a wolf, who will either have a shield mane or hold a sword like Great Wolf Sif. Don't recall its name
Dynamaxing and Gigantamaxing are new dynamics that will supersize pokemon in specific areas. Gigantamaxing is different from dynamax as it changes what the Pokémon looks like. Meowth looks like long cat.Lapras gets layers like musical bars to its shell and musical notes. Pikachu looks like retro fat Pikachu
Sonia is Leon's former rival who is researching the dynamax phenomenon at the behest of her grandmother and professor of the game.
Some Pokémon, like Farfetch'd, will get regional evolutions, like Sirfechtd. Meowth looks like a ball of spiky grey fur
Skwovet and Greedunt are chipmunk Pokémon who will hide in berry trees and attack randomly if you shake for too many berries. If they attack, you lose half the berries that dropped.
The fourth gym is the first Fairy type gym, led by an actress named Opal. Milo, Nessa, and Kabu are the first ones.
Before fighting the gym leaders, you have to complete the gym challenges.
Milo has you herding sheep Pokémon named Wooloo, but Pamper, an electric corgi Pokémon, will startle them and send them rolling elsewhere.
Nessa has you running through a maze where water blocks the way
Kabu requires you to catch Pokémon and get five points, but you have to be in a party battle with another trainer who's also trying to catch it
While there is a transit system, you will have to go through the Wild Area at times, an open world biome that has a weather system and little pockets where wild Pokémon dynamax and have to be beaten in a for person raid. You will randomly see nearby players and interact with them to get their league cards and items
Camping is how you play with Pokémon now. You'll get two toys, a feather toy and toy pokeball, which can raise friendship. You can make curry which will raise starts and friendliness
Pokémon will not walk beside you in the overworld map
Scorbunny will have fighting moves, but is pure fighter [NOTE: Might mean Fire]. It becomes Raboot, but I don't remember the final evolution, except that it looks like a fighter. It looks humanoid
Sobble becomes Sizzile and then Intelleon, a chameleon with a spy theme
Grookey will end up as a giant gorilla that beats a wood drum to attack.
The best Pokémon so far is the blue seagull who when it dives, either gets a barracuda in its mouth or a pikachu, which it launches at its enemy
I really don't like Sobble's 2nd form. That color scheme is just terrible. Sobble's last form? Not sure if I'll like it or not, but it's definitely better than the alleged second form. Grookey's final evo isn't offensive to me, though.
Edit: Latter colors are just photoshops of shiny, true colors are posted in next post
alleged Galar dex (TAKE WITH A GRAIN OF SALT; PROBABLY FAKE)
I really like Sobble's final form, and Grookey being an ape actually looks pretty good. I'm crossing my fingers for Scorbunny though, I really hope she has a good final form too because other than that, I'm liking these starters so far. Don't have any strong opinions on the new Pokemon and new Meowth form, they're bland to me as far as I'm concerned.