Gym Leaders are replaced with "Team Captains" and the Elite 4 will be replaced by "Island Leaders".

After the league is established there will be an Elite 4

There are No Gyms and there is No League. One plot point is that the Professor guides the hero in creating the League

The new wristband allows all abilities to become stronger and can load "Adventurine" stones according to the game version. There will be a lot of these stones me you need to collect them, and some Pokemon can only transform with the "Adventurine" stones. Ash Greninja relies on this mechanic to transform

Basically every Pokemon can be ridden with the new riding feature

There are a bunch of unmarked places on the map known as "Districts" in which there are really though Pokemon known as "Overlords"

Rockruff becomes a werewolf, Rowlet an Archer, Litten a Wrestler, and Popplio a Siren (That art of the final starters floating around may just a bunch of good guesses. It may be fake)

There will be a Mushroom, Snowman, Rugby/Football Monkey, Sea Cucumber, and Dolphin Pokemon
Marshadow is a new legendary with a very special type

So the info is still kinda the same which is pretty interesting and yeah, I do agree on the last part, they have been on those forums for a long time so there's like no reason for them to lie. I still believe that those artworks are nothing but beta designs and quite possibly not how the final forms will look like, but still if they are a guess, they are a really dam good one.

Also, someone here posted some very interesting info earlier this morning (at least in my time lapse) about alleged info that was shared by an individual from a translation team. I can't link the thread since it unfortunately got deleted. But there were some very interesting info there, like Wimpod being the Gyarados/Milotic of this gen and its evo looking like a Scolipede/Kabutops hybrid or some pokemon like Bruxys not having an evo or pre-evo or Rockroff evolving depending on the starter you pick. This bit reminded me of your previous post where the newer leaks say Rockroff has more then one evo and combined with the types found on the site and Rockroff's connection with the starters, this is the conclusion I reached:

Rockroff will have a total of three evolutions and they will all be influenced by the starters, Rock/Ground if you pick Rowlet, pure Rock if you pick Litten and Rock/Fighting if you pick Popplio.

Mudsdale and Drampa have pre-evos

The third guardian looks just like the Souvenir

like I said, Bruxish and Mimikyu and someone else don't have evos or pre-evos

the entire starter based evolution with Rockroff

Cutiefly evolves into a hawk moth

there's a new battle style were two pokemon "merge" to become more powerful (this I'm HIGHLY skeptical about)

there's a shovel pokemon and three based on the rock-paper-scissors game

Salandit has a gender split evolution

the entire diamond mechanic and how it also involves Ash-Greninja.

It's very fuzzy cause I barely woke up when I first saw it. But basically the diamond mechanic works like you go in like a quest to find the diamonds and it powers up moves and such. And if I remember correctly, it also said it amplifies the power of the abilities of the pokemon. And for the merge battles, again, very fuzzy, but basically is like I said, two pokemon merge to form a more powerful one in battle, kinda like the Gems in Steven Universe. And i also remember it said "like the guardians", so this could confirm the theory that the Island Guardians like Tapu Koko do indeed form a totem pole.
And I just remembered more !

Lilly is the key to the main story and also to perfect Zygarde

aside from Zygarde, there's a total of 7 Legendaries involved in the story, so basically Lunala/Solgaleo/Marshadow and the guardians.

Discussed on Friday's Trailer:
New:
Wishiwashi (Solo Form)
Wishiwashi (School Form)
Pyukumuku
Morelull

Team Skull Grunts:
Plumeria
Guzma

New Alola Forms:
Meowth
Marowak
Raichu