Krobelus, the "Orange Islands" existed only in the anime, and when they were later adapted into the games, they became the Sevii islands in FireRed and LeafGreen. Adding the Orange Islands as a region would be going against the canon of their existence as the Sevii Islands.
Also, you can't change wild pokemon in regions that have already been established. If I'm walking around outside Saffron City I can come across a Growlithe because they're native to the region, but if I see a Hoppip flying around, it's going to either belong to a trainer or it is seriously lost.
Also, you can't change wild pokemon in regions that have already been established. If I'm walking around outside Saffron City I can come across a Growlithe because they're native to the region, but if I see a Hoppip flying around, it's going to either belong to a trainer or it is seriously lost.