Mod Edit: Please keep Sevii Island discussion in the Sevii Island thread. Thank you.
FireRed and LeafGreen was released ten years ago. Ruby and Sapphire are getting remakes in the form of OmegaRuby and AlphaSapphire. FireRed and LeafGreen was in the same generation as Hoenn. Emerald borrowed some stuff from FireRed and LeafGreen. HeartGold and SoulSilver had stuff from Crystal. So maybe OmegaRuby and AlphaSapphire can have stuff from FireRed and LeafGreen. Here's what I want in OmegaRuby and AlphaSapphire.
Sevii Islands. Got a whole forum about it. The Sevii Islands was a chain of islands exclusive to FireRed and LeafGreen as a post-game area. There you can catch Johto Pokémon to fill your National Pokédex. In the Hoenn remakes, you can also catch Sinnoh, Unova, and Kalos Pokémon. You don't find any Hoenn Pokémon because they can all be caught on the mainland.
Team Rocket. Don't worry, Team Magma and Aqua will return as the main antagonists in the main story. But Team Rocket should be the villains of the post-story Sevii Islands quest. It seems Team Rocket doesn't give up. Heck, there is one time in their scheme where they go to Hoenn.
Kanto Gym Leaders. They can be fought at the Trainer Tower. And for something more epic, on certain days of the week, a Kanto Leader can team up with a Hoenn Leader in gym rematches!
References to FireRed and LeafGreen events as happening a month ago.
Battle against Red on the top of the Trainer Tower.
Pokémon availability in the Sevii Islands is based on FireRed for OmegaRuby and LeafGreen for AlphaSapphire.
Teachy TV obtained as a gift from Prof. Birch along with your Pokédex and Poké Balls. The Poké Dude's Pokémon is replaced with Hoenn Pokémon.
Black and white flashbacks when you continue a saved game.
A help menu when you hit L or R.
Location data will be available for Kanto locations. Plus Johto, Sinnoh, Unova and Kalos. They're not accessable, but the caught locations of the Pokémon can be read even if they were transferred all the way from Gen III. If you had a starter Charmander in FireRed that evolved into Charizard, the location data will list "Pallet Town". Transfer it to Pal Park, and it will say "Kanto". Send it to Unova, and it will still list "Kanto". Put it into Pokémon Bank to transfer it to OmegaRuby/AlphaSapphire and it will finally say "Pallet Town" again.
During the Kanto Leader battles at the Trainer Tower, a remix of the FireRed/LeafGreen Leader theme plays, except for Blue who has his Champion theme.
Kanto will NOT be accessable. We've already been there a lot. At least there's Sevii.
The Legendary Birds will be catchable. Moltres is in it's same spot on Mt. Ember. Articuno in Icefall Cave. And Zapdos in New Mauville.
The Four Island Day-Care is replaced with Friend Safari.
The Altering Cave on Route 103 is removed in favor of the Altering Cave on Outcast Island.
You can sometimes find Bruno and Brawly at Sevault Canyon.
Suicune, Entei and Raikou roam the Sevii Islands. Which one you get depends on your Hoenn starter.
Well, that's all I can think of.