Fans now know that Pokémon FireRed and LeafGreen are not the original ROM data on the Switch. They were recompiled from the ground up to add new features, such as allowing you to easily get Deoxys, Lugia, and Ho-Oh.
Meatball_132 shared another interesting insight:
I found a function that initialises the emulator hacks based on the GBA ROM’s ID.
These are the IDs the emulator recognises for the Pokemon hacks. BPR and BPG are FireRed and LeafGreen, respectively, but AXV, AXP, and BPE are Ruby, Sapphire, and Emerald, respectively. Huh.
Pokémon FireRed and LeafGreen use the same Game Boy Advance emulator used in Nintendo Classics, an in-house program called Sloop. These games use a fork of Sloop in such a way that they can only work with each other.
So, what does it all mean? It suggests that these games can interact with Pokémon Ruby, Sapphire, and Emerald. Or at least, that’s the plan.
And yes, that suggests that Nintendo and The Pokemon Company will release those games in the future. But we can’t know if those plans change, so nothing’s confirmed until it’s official.