This is going to be long. These are mainly things I'd like to see in any future game & I wouldn't expect this all to be able to fit in 1 game lol.
1. Male fairy type specialists (cough cough - Ilima & Mina being switched last minute - cough cough)
2. Fairy type elite-four
3. Gyms that are conceptual with their specialty pokemon, not just based off of their type. Like weather, environment, their abilities or design being the gym concept etc... or specializing in 2 types
4. Normal type specialist that has all pokemon with a different secondary type would be cool
5. Pokemon contests (or something like it) being brought back with more detail & immersiveness. Or the ability to not HAVE to be a pokemon trainer to go through the game, being able to pick your own path a little more. There are a lot of pokemon-paths in the universe other than just battling (although battling still being necessary in game, just not gaining gym badges & elite four if you chose to be a coordinator or something etc..)
6. A less linear & concrete story. More options & choices to how you wanna play the game.
7. A LIITTTLE bit more mature of a tone would be nice. Not with violence or anything, but the simplicity of the games is even a little too simple for even a lot of preteens & older kids. Especially since a GIANT part of pokemon revenue comes from adult/teen fans. It makes the characters feel less like people, with character development being kinda bland & overly childish. It's like your being babied the whole time. (also not playing a 10 year old would be nice. I think the age should be like 16 or so)
8. Ability to BE a gym leader, after the game ends, would be cool. Play with others online at their gyms etc... kinda like secret bases.
9. More unique type combos. Grass/Fire, Dark/Fairy etc... or more pokemon of type combos that are very rare
10. More pokemon based off of animals we've never seen in pokemon, Dolphins, Peacocks, etc...
11. Evolutions (or something new) for some pokemon that are almost useless is battle. Corsola, Delcatty, Dunsparce. (unless they bring something to pokemon where battling isn't the ONLY thing you can do in pokemon. Having your favorite pokemon being mediocre/terrible in battle suuucks)
12. Rideable pokemon that are in your team
13. More customizing options + character customization that isn't gender-locked. Boy clothes & hairstyles are really boring & limited, IMO. I see nothing in my style for boys, ever >__> Let me havvee knee high socks or cute bags pleeeassee
14. Picking a pokemon that can walk with you in 3D. I want to feel more like my pokemon aren't just battle pawns, ya know.
15. Feeling your fame rise throughout the game. More people start knowing who you are etc.. as the game goes on, and the reactions you get are tailored to what you actually have done in the game / your choices.
16. NPC dialogue that isn't limited to like 1 phrase per person. It would be nice to be able to have more personality in random people. Also maybe making it so different people actually look different.
17. The ability to have your own house or area in the game you customize a bit (if not a gym).
18. A region based off of California, or the west coast of the US. Or a region based off of a huge load of mixed things. Different cities in game based off of different places IRL entirely. A region that has different cultures based on different cities/ areas.