1. Team Magma's Hideout be the Emerald version, not the Ruby one. It never made sense why a team hell bent on expanding the land had a base on the SEA that you had to SURF to. How did they get there anyway? What on their teams could SURF? And why are they training Wailmer? Ugh.
2. Elite Four rematches. I'd like for them to level up like how they do in newer games. I liked what they did with the gym leader rematches though, so I hope those remain the same, but just make them more frequent so you don't have to wait around for them so often.
3. More variety for the evil organizations. Pull some Pokemon that they had in the TCG, if anything. Those were good and varied, like Team Magma's Claydol. That's a good card too, btw.
4. Let Brendan/May fully evolve their starter. I know someone mentioned that they weren't meant to show you up in battle usually, but they still seemed hurt at a loss. Scott mentions that they're red in the face when you beat them before getting to Fortree, so they clearly care, just not to the extent of, say, Blue or Silver. Even though they try to work on the Dex for their dad, you think that'd mean they'd have a final stage starter. At least give them that much, GameFreak.
5. Rivals in mind, give Wally a better presence as a rival. I feel like he had great potential, but with only two battles in the main story, I feel like he could use some work. I think two battles makes sense, because we see just how much he's grown over all of this time in between the two battles, but at least more contact with him or some tag battles at some point would be pretty interesting. I won't be too upset if we don't see him more in battle, because like I said, it makes sense, but I'd at least like for him to show up more often and have more of a rival role to a better degree of what he had in RSE.
6. Add Emerald post-game Safari Zone Pokemon to the main areas. I want more variety in the wild life in ORAS than what RSE gave us. Sure, it was a lot, but many of those Safari only Pokemon Emerald gave us were pretty good! Like Mareep, Houndour, and Wooper. I'd like to see those in the region, and going back to the evil teams, Houndour and Wooper would be a nice addition for Magma and Aqua respectively!
I think that's all I have for now!