I think there's a good reason why they haven't done a whole second region and instead have opted for a smaller, mini region that is somewhat isolated from the core region.
Gen 2 and their respective re-makes suffered from horrible level imbalances where even playing with a full team of 6 will leave you lagging a bit behind the Gym Leaders by the 4th or 5th gym, and VERY underleveled for the E4 and Red because, for 80% of the game, you're fighting Pokemon in their mid 20s, and the highest wild Pokemon level is in the 30s.
And then by the time you reach Kanto, it's STILL filled with level 1, level 5, level 10, etc.. Pokemon, the Gym Leaders mons are in their 20s and 30s, you're ALREADY a champion with presumably a full team that's mostly evolved with high powered moves, and they present no real challenge.
Compare that with the Sevii Islands, or Battle Zone, or the Battle Frontier area in Emerald, Eastern Unova. New Pokemon, usually expands on the plot, a bit, higher levels from both NPCs and wild Pokemon, and, since Gen 4, usually new stuff opens up in the old areas of the region as well.
I'm all against this whole multi-reigon wankery. It's abo****ely ludicrous and violates the core principle of keeping Pokemon simple and easy to "beat" for the casual player, which is most of its audience.