Okay, let's recap:
1. Player Health Bar - It would have been so much easier if we could see how much damage was being dealt, because the screen turning black/red just isn't enough. If player damage returns, we need a health bar.
2. Optional Tutorials - For the love of GOD make the tutorials optional! At least half the fandom has been playing these games for a decade or more. We don't need to be instructed on what to do, even for a game like Legends. For those that do feel they need it, it can be there.
3. Human v. Human Combat - While this will completely change Pokémon forever, I feel it is a necessary change. It's time the humans fought alongside their partners, and with that, allow humans to take damage for their partners.
4. Uncatchable Legendaries - I've mentioned this before and I'm sticking to it. Legendaries should not be obtainable in-game. It doesn't make sense even in the Pokémon universe for a mere human to catch a literal god. All legendaries should be received via Mystery Gift or other downloadable means.
5. Boss Level Curve - I think it's time the bosses got tougher as we do. The same should apply to gyms. A good example would be the level of a gym's team will always be 2-5 levels higher than the player's. Even better, all gym leaders will have 8 preset teams, and the team used will be relative to the number of badges the player has upon battle.
6. Travel Marker - Similar to Breath of the Wild's Hero Path Mode, it would greatly help if players could keep track of where they are/were going on the map. It gets rather difficult to backtrack in Legends because I can't remember precisely where I was or where I've been. A traveling line, even a temporary one, would be a great help.
7. Varying Outcomes - While keeping it streamlined for younger/newer players, Pokémon games should have a forked outcome pathway that decreases the accessibility to victory. Of course, open world gameplay does this on its own. However, losing gym battles should actually impact progress, and failing to defeat the Champion should remain fixed. Conversely, becoming Champion should require you having to defend your title, and should you lose it, you'll have to battle for it again.
8. Preset "Hidden Moves" - Something that would really streamline the games is if all Pokémon came with 'Hidden Moves,' just like they come with Abilities, to allow ease in traveling throughout a region. Instead of relying on special Riding Pokémon, every creature will have at least one preset task they can do. Pidgeot and Drifblim will always be able to fly you around; Gyarados and Empoleon will always be able to carry you over water, and Hariyama and Lucario will always be able to knock down walls and boulders.
9. Traditional Yawn - Given my love for using the move in competitive play, I'm not too fond of this new form of Yawn. I do hope the original move remains in Gen 9.
10. Robust Training Grounds - I do like how there's a place where we can battle to practice, so I would love it if in Gen 9 there was a whole facility dedicated to training and learning, especially for 'competitive play.' They could even have the Hyper Training/Grit Rock person there.
I doubt most of these will happen lol, but it would be nice. The one I really do wish would come to be is the boss level curve. If open world gameplay is to continue, there must be a way to prevent overlevelling our team.