I am working in the next game currently, can't tell you my position but here is what I know:

The next game is a Generation 4 remake, by making it Game freak had in mind to deliver the "ultimate remake experience in a modern software", those are their words but not sure how fans will respond to it.
Sinnoh is a big region compared to Galar, therefore they made the choice of reusing the Pokémon Lets Go artstyle.

-Game is a simplified version of the original games, it is a Diamond/Pearl remake, therefore there is no Battle frontier or Distortion world
-320 mons are in : the Platinum dex is reused, Johto and Hoenn starters and box legendaries are in. Lots of gen 3 and gen 2, but no mons past gen 4 are included
-Dialga and Palkia get new forms, Dialga is purple and gets wings that are tied to an amethyst on his neck, look like a western dragon. Palkia is basically the same as the original but red, he gets some shark atributes such as fangs and a huge tail. The Lake Trio share a unique fused form called Angelic form
-No new regional forms, but Mega evolutions of existing mons are back
-The underground was entirely remade, works like wild area but no free camera. Some dungeons and routes such as Mt Coronet/Solaceon ruins have been retconned to be easier to cross. You no longer need HMs since they are gone but there are still some barriers; therefore you'll need to use different functionalities included in your Rotom bag
-Some cut moves like Hidden Power are back
-You can ski with your Pokémon in a new snowy area around Route 217
-Character customization is gone, but you can get different hats and scarves as you travel to different cities
-Gyms are back, Contest buildings were expanded to look like Galar stadiums, they work basically like the ORAS contests; you can no longer dress your Pokémon
-Leon Cameo in Sunyshore city

Nothing more I know but theres probably some points I've missed. Expect the game to be revealed around May, since it is how it works with remakes.