Update: Nintendo has good news for North American Pokemon fans. Japan may be getting Black/White 2 first -- as soon as this summer -- but folks in the States and Canada need only wait a few additional months for the games. For us, the Black and White sequels will be arriving this fall.
You can set aside all the Pokemon color/gem jokes, because the next Pokemon title will be (Surprise!) a numerical sequel. Unexpected, right? Pokemon Black/White 2 was just announced via Japanese TV show Pokemon Smash.
The upcoming sequels to Black and White are set to hit Japan this June for Nintendo DS, with no mention of release windows for other regions. Nintendo has yet to name any new Pokemon or gameplay changes. Seriously though, how many more new Pokemon can they come up with at this point?
Black/White 2 will be the first numbered installments in the core series, as previous follow-ups are generally given an "enhanced" name rather than numbers (i.e. Pokemon Pearl and Diamond succeeded by Platinum). So technically, you could say this is the first occurence of Pokemon sequels.