1 or 2, on the condition that working on them means making the AI better at using them.
If I can get creative with 5, I want Pokemon riding taken further down its logical route. I think I speak for at least quite a few of us when I say I'm sick of HMs. The Pokemon company clearly heard some of the complaining, given the changes made to games starting with SM, but in my opinion, the problems aren't really fully solved.
The biggest problem for me wasn't that Pokemon move slots had to be wasted on HM moves (and Rock Smash), that not enough Pokemon could use them, or that some of the moves sucked in battle. That problem peaked in Hoenn, because of how much of it was either water or mountains, but it's regressed ever since. The biggest problem for me is that making progress dependent on getting HM moves and being allowed to use them out of battle ruined the illusion of being on an adventure with fantastic creatures. When I'm constantly being dazzled with sparkly visuals and talk of what Pokemon can do, I don't want what they can do limited to certain situations. In that respect, sadly, SM/USUM didn't really fix anything with how they replaced HMs, nor are LGPLGE looking to fix them. As it stands now, you still have to wait until the plot says so to ride Pokemon and use their abilities.
I don't like that. When I obtain a Pokemon that's supposed to have super strength, I don't it to be unable to move heavy objects until it learns a move, nor do I want its supposed abilities to be rendered useless by summoning another Pokemon with super-strength; a Pokemon that isn't mine and that only performs feats related to said strength, and then leaves. I want to ride my own Pokemon, to use my own Pokemon's abilities to conquer obstacles, and I want to be able to do that, when or where I want, without plot limitations, and I want several options. An obstructive tree that could be cut down, should also be able to be burnt down. An obstructive Snorlax that could be woken with a Poke flute should also be movable by a strong enough Pokemon. Basically, get rid of all the locks and keys you can, in favor of a physics system that invites exploratory play, and instead use overpowering opponents and an event system to dictate the game's flow.