A drawback in Black and White and something I don't think was taken well by old fans was that we had no access to obtaining old Pokémon until post-game. This is something they managed to fix in Black 2 and White 2. Even though the region is set to take place in a different country away from where Unova and the rest of the regions are located, it doesn't necessarily mean that old Pokémon have to be cut off like they originally did in Black and White.I am a little skeptical on past pokemon in regional dex. I am a little cunfused honestly. The region is in France/Europe yet we saw old pokemons in the trailers. What's up with that ?
Black and White were more or less a reboot to the franchise, so they wanted us to play the games like they were a brand new start completely. Since we're now passed the reboot, and GameFreak is now evolving the world of Pokémon as they say, it only makes sense to at least include some of those old Pokémon for fans to use.