Some useful stuff we know:

>All Pokémon Centers will have a Name Rater & Move Deleter/Relearner
>Relearner does not require Heartscales
>Gigantamax shuffles stats around like Mega Evolution, Dynamax is just a overall stat boost
>Auto-save feature can be toggled on/off, useful for when hunting certain Pokémon
>Wild Pokémon with a yellow aura indicates it having some perfect IVs & possibly some egg moves
>New feature allows certain "parameters" to be changed to help Pokémon useful for battle (i.e. Natures)
>Certain abilities such as Moody will be adjusted for balance
>"Surprise Trade" will be an instant Wonder Trade the player can do as they're adventuring
>PC Link Box allows you to access your PC anywhere (supposedly limited to Wild Area)
>Rating Battle will no longer be based on number but instead a Ranking system

Feel free to mention anything else you find useful, like Gastrodon having Earth Power which means updated egg move/movepools or possibly having tutor moves in a first version game.