What I want in a Pokemon game for Gen 10/Gen 5 remake:
-More in-depth and meaningful story/characters

-HGSS/Let's Go following Pokemon. I like having my lead mon/starter following me around. It makes them feel more like a companion.

-Difficulty slider:
Easy = Gen 8-9 level difficulty, rare items are easy to find, Pokemon EV training is easier. For people who want to have a chill, relaxing time.
Medium = Gen 3-4 level difficulty. Rare items are harder to find. For people who want a bit of a proper challenge and some grinding.
Hard = Radical Red/Dark Rising level difficulty. Rare items are hard to find or cost a lot. Items become crucial. For those who like hardcore gameplay, nuzlockes, etc.

-Rare items being actually rare. Getting EXP candies, vitamins, and rare candies as easy as they are makes grinding a mon to level 100 a bit cheap IMO.

-Retcon the 'Mega evolution is abusive/detrimental to the Pokemon' trope, then re-add Mega evos, perhaps as a later on addition, perhaps after the Elite 4.

-LEGENDS: KYUREM. I'd love the Gen 5 remakes to be another Legends game, with the same mechanics for battle as PL:A. Have its story tie into Gen 9 games/Terastallization phenomenon, time travel mechanics, maybe we have access to some of the paradox Pokemon, add in the potential for the original Tao dragon before it split into Kyurem, Zekrom, and Reshiram, and have us relive that tale.

-Better and unique animations for moves.

-Proper addressing of bugs, or even better, make sure there are minimal bugs to begin with. Good god, SV on release was beyond buggy xD

-Good meta for high level/comp play.

-Ability to go to the main professor that you start with and ask for a Pokemon to practice with them and see how they would fare against literally any Pokemon. Maybe as a holographic fighting simulator. That way you can get a feel for the mon and see how they would fare against other mons and then go catch accordingly.

-More unique mons, less past mons. Maybe some community made fakemons become actual Pokemon with royalties going to the person who made them.

-Certain choices can affect certain outcomes of the story's progression.

-Add a little suspense or spook factor to the game. Think Lavender Town tower but a bit scarier.