I'd love to see a re-imagining or sequel to the original games. 20 years has passed, new Pokemon have been discovered and so on, so these are just my thoughts on what the games could include:
A new playable character, possibly starting in a new town (much like B2W2)
The original 3 starters with updated movesets
A new rival character, preferably that we get to name
Changes to gyms and gym leaders over time - Viridian Gym is obviously no longer under control of Giovanni, and instead the Pokemon League have installed a new trainer, maybe fighting the gyms in a different order
Changes to towns and cities - some have grown, some have shrunk
Inclusion of Sevii Isles, Johto and Mt Silver
Expanded Pokedex - Houndour in Kanto, Porygon's evolutions